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Fair Value of Financial Assets and Liabilities Fair Value of Financial Assets and Liabilities - Fair Value Measurement of Assets and Liabilities, Recurring and Nonrecurring (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability, Current $ (232) $ (282)
Derivative Liability, Noncurrent (409) (392)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]    
Derivative, collateral, right to reclaim cash 77 29
Derivative Instruments Not Designated as Hedging Instruments, Asset, at Fair Value 0 (2)
Derivative Asset, Notional Amount 811 933
Margin Deposit Assets (117) (158)
Cash and Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 389 360
Restricted cash member [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 145 180
Other assets    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 85 25
Nuclear Decommissioning Trust Fund Investments [Member]    
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]    
Fair Value Net Assets Liabilities Excluded From Nuclear Decommissioning Trust Fund Investments (82) (31)
Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [1] 656 373
FinancialAssetsFairValueDisclosure1 15,716 13,253
Deferred Compensation Liability, Current and Noncurrent (145) (136)
Financial Liabilities Fair Value Disclosure (786) (810)
FinancialAssetLiabilitiesNetFairValueDisclosure1 14,930 12,443
Alternative Investment, Fair Value Disclosure 3,534 3,113
Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (637) (662)
Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (4,040) (4,697)
Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (53) (79)
Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability [2],[3] 3,456 4,114
Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (4) (12)
Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (2) (10)
Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (9) (21)
Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability   (4)
Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 7 23
Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure [4] 13,431 11,092
Alternative Investment, Fair Value Disclosure [4] 3,510 3,049
Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [5] 220 129
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 7,254 6,014
Alternative Investment, Fair Value Disclosure 2,176 2,011
Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 4,736 3,977
Alternative Investment, Fair Value Disclosure 510 493
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 1,865 1,804
Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 1,969 1,320
Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 82 37
Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 263 264
Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure [6] 557 552
Alternative Investment, Fair Value Disclosure [6] 510 493
Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 528 498
Alternative Investment, Fair Value Disclosure 131 71
Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 222 148
Alternative Investment, Fair Value Disclosure 222 148
Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 471 326
Alternative Investment, Fair Value Disclosure 471 326
Fair Value, Measurements, Recurring [Member] | Pledged Assets For Zion Station Decommissioning [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 39 113
Alternative Investment, Fair Value Disclosure 24 64
Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 2 11
Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 1 2
Fair Value, Measurements, Recurring [Member] | US Treasury And Government Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure   17
Fair Value, Measurements, Recurring [Member] | MiddleMarketLending Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 36 83
Alternative Investment, Fair Value Disclosure 24 64
Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 240 224
Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 77 74
Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 58 50
Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 12 16
Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 93 84
Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 1,304 1,381
Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 4,225 5,092
Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 68 76
Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset [2],[3] (2,989) (3,787)
Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 9 28
Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 6 16
Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 10 28
Fair Value, Measurements, Recurring [Member] | Proprietary Trading Interest and Currency Derivative [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset   5
Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset (7) (21)
Fair Value, Measurements, Recurring [Member] | Other Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 37 42
Fair Value, Inputs, Level 1 [Member]    
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]    
Derivative, Fair Value, Amount Offset Against Collateral, Net 65 71
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [1] 656 373
FinancialAssetsFairValueDisclosure1 6,980 5,674
Deferred Compensation Liability, Current and Noncurrent 0 0
Financial Liabilities Fair Value Disclosure (63) (37)
FinancialAssetLiabilitiesNetFairValueDisclosure1 6,917 5,637
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (64) (37)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (713) (1,267)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (2) (3)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability [2],[3] 651 1,233
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 1 0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0 0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (1) 0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability   (4)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 2 4
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure [4] 6,215 4,952
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [5] 135 110
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 4,163 3,551
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 1,917 1,291
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 1,917 1,291
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure [6] 0 0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Pledged Assets For Zion Station Decommissioning [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 2 27
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 2 11
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury And Government Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure   16
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | MiddleMarketLending Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 135 124
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 77 74
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 58 50
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset (26) 197
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 557 1,358
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 2 3
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset [2],[3] (585) (1,164)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset (2) 1
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 0 0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 0 0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Interest and Currency Derivative [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset   3
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset (2) (2)
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 2 [Member]    
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]    
Derivative, Fair Value, Amount Offset Against Collateral, Net 320 197
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [1] 0 0
FinancialAssetsFairValueDisclosure1 3,793 2,937
Deferred Compensation Liability, Current and Noncurrent (145) (136)
Financial Liabilities Fair Value Disclosure (329) (237)
FinancialAssetLiabilitiesNetFairValueDisclosure1 3,464 2,700
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (179) (89)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (2,226) (2,378)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (42) (50)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability [2],[3] 2,089 2,339
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (5) (12)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (2) (10)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (8) (21)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability   0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 5 19
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure [4] 3,058 2,414
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [5] 85 19
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 915 452
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 2,058 1,943
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 1,614 1,554
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 52 29
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 82 37
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 263 264
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure [6] 47 59
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Pledged Assets For Zion Station Decommissioning [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 1 3
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 1 2
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury And Government Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure   1
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | MiddleMarketLending Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 83 80
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 12 16
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 71 64
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 640 413
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 2,378 2,505
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 31 50
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset [2],[3] (1,769) (2,142)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 11 27
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 6 16
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 10 28
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Interest and Currency Derivative [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset   2
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset (5) (19)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 3 [Member]    
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]    
Derivative, Fair Value, Amount Offset Against Collateral, Net 81 61
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [1] 0 0
FinancialAssetsFairValueDisclosure1 1,409 1,529
Deferred Compensation Liability, Current and Noncurrent 0 0
Financial Liabilities Fair Value Disclosure (394) (536)
FinancialAssetLiabilitiesNetFairValueDisclosure1 1,015 993
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (394) (536)
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (1,101) (1,052)
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (9) (26)
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability [2],[3] 716 542
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability   0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure [4] 648 677
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [5] 0 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 251 250
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 251 250
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure [6] 0 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 397 427
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Pledged Assets For Zion Station Decommissioning [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 12 19
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury And Government Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure   0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | MiddleMarketLending Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 12 19
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 22 20
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 22 20
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 690 771
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 1,290 1,229
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 35 23
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset [2],[3] (635) (481)
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 0 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 0 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 0 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Interest and Currency Derivative [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset   0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 0 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 37 42
Exelon Generation Co L L C [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability, Current (211) (263)
Derivative Liability, Noncurrent (174) (153)
Derivative liabilities, fair value [7] 349 333
Exelon Generation Co L L C [Member] | Cash and Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 259 252
Exelon Generation Co L L C [Member] | Restricted cash member [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 127 157
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [1] 168 39
FinancialAssetsFairValueDisclosure1 15,035 12,718
Deferred Compensation Liability, Current and Noncurrent (38) (34)
Financial Liabilities Fair Value Disclosure (423) (450)
FinancialAssetLiabilitiesNetFairValueDisclosure1 14,612 12,268
Alternative Investment, Fair Value Disclosure 3,534 3,113
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (381) (404)
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (3,783) (4,439)
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (53) (79)
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability [2],[3] 3,455 4,114
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (4) (12)
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (2) (10)
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (9) (21)
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability   (4)
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 7 23
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure [4] 13,431 11,092
Alternative Investment, Fair Value Disclosure [4] 3,510 3,049
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [5] 220 129
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 7,254 6,014
Alternative Investment, Fair Value Disclosure 2,176 2,011
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 4,736 3,977
Alternative Investment, Fair Value Disclosure 510 493
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 1,865 1,804
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 1,969 1,320
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 82 37
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 263 264
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure [6] 557 552
Alternative Investment, Fair Value Disclosure [6] 510 493
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 528 498
Alternative Investment, Fair Value Disclosure 131 71
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 222 148
Alternative Investment, Fair Value Disclosure 222 148
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 471 326
Alternative Investment, Fair Value Disclosure 471 326
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Pledged Assets For Zion Station Decommissioning [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 39 113
Alternative Investment, Fair Value Disclosure 24 64
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 2 11
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 1 2
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury And Government Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure   17
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | MiddleMarketLending Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 36 83
Alternative Investment, Fair Value Disclosure 24 64
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 50 39
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 5 2
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 23 19
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 22 18
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 1,304 1,381
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 4,225 5,090
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 68 76
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset [2],[3] (2,989) (3,785)
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 6 12
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 3 0
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 10 28
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Interest and Currency Derivative [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset   5
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset (7) (21)
Exelon Generation Co L L C [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 37 42
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [1] 168 39
FinancialAssetsFairValueDisclosure1 6,385 5,237
Deferred Compensation Liability, Current and Noncurrent 0 0
Financial Liabilities Fair Value Disclosure (63) (37)
FinancialAssetLiabilitiesNetFairValueDisclosure1 6,322 5,200
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (64) (37)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (712) (1,267)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (2) (3)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability [2],[3] 650 1,233
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 1 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (1) 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability   (4)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 2 4
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure [4] 6,215 4,952
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [5] 135 110
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 4,163 3,551
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 1,917 1,291
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 1,917 1,291
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure [6] 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Pledged Assets For Zion Station Decommissioning [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 2 27
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 2 11
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury And Government Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure   16
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | MiddleMarketLending Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 28 21
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 5 2
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 23 19
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset (26) 197
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 557 1,356
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 2 3
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset [2],[3] (585) (1,162)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset (2) 1
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Interest and Currency Derivative [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset   3
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset (2) (2)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [1] 0 0
FinancialAssetsFairValueDisclosure1 3,729 2,859
Deferred Compensation Liability, Current and Noncurrent (38) (34)
Financial Liabilities Fair Value Disclosure (222) (135)
FinancialAssetLiabilitiesNetFairValueDisclosure1 3,507 2,724
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (179) (89)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (2,226) (2,378)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (42) (50)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability [2],[3] 2,089 2,339
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (5) (12)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (2) (10)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (8) (21)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability   0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 5 19
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure [4] 3,058 2,414
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [5] 85 19
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 915 452
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 2,058 1,943
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 1,614 1,554
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 52 29
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 82 37
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 263 264
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure [6] 47 59
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Pledged Assets For Zion Station Decommissioning [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 1 3
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 1 2
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury And Government Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure   1
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | MiddleMarketLending Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 22 18
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 22 18
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 640 413
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 2,378 2,505
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 31 50
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset [2],[3] (1,769) (2,142)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 8 11
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 3 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 10 28
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Interest and Currency Derivative [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset   2
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset (5) (19)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [1] 0 0
FinancialAssetsFairValueDisclosure1 1,387 1,509
Deferred Compensation Liability, Current and Noncurrent 0 0
Financial Liabilities Fair Value Disclosure (138) (278)
FinancialAssetLiabilitiesNetFairValueDisclosure1 1,249 1,231
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (138) (278)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (845) (794)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability (9) (26)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability [2],[3] 716 542
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Derivatives Designated As Hedging Instruments Liabilities [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | EconomicHedgingInstrumentLiabilites1 [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Liabilities Interest and FX [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability   0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effect of Netting and Allocation of Collateral Interest Rate and FX Liabilities [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Nuclear Decommissioning Trust Fund Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure [4] 648 677
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents NDT [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [5] 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 251 250
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 251 250
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury and Government [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | State and municipal debt [Domain]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Income [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure [6] 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Middle market lending [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 397 427
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Private Equity Funds [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Real Estate Funds [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Pledged Assets For Zion Station Decommissioning [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 12 19
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalent Zion [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Funds Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | US Treasury And Government Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure   0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | MiddleMarketLending Zion Decom [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 12 19
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Commodity Derivative Assets [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 690 771
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 1,290 1,229
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 35 23
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset [2],[3] (635) (481)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate and Foreign Currency Derivative Assets [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Designated as Hedging Instrument [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic hedge Interest and Currency [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Proprietary Trading Interest and Currency Derivative [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset   0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | EffectsofNettingandAllocationofCollateral1 [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Asset 0 0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 37 42
Commonwealth Edison Co [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability, Current (21) (19)
Derivative Liability, Noncurrent (235) (239)
Commonwealth Edison Co [Member] | Cash and Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 45 36
Commonwealth Edison Co [Member] | Restricted cash member [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure   2
Commonwealth Edison Co [Member] | Other assets    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 62  
Commonwealth Edison Co [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [8] 98 20
FinancialAssetsFairValueDisclosure1 98 20
Derivative Liability [9] (256) (258)
Deferred Compensation Liability, Current and Noncurrent (8) (8)
Financial Liabilities Fair Value Disclosure (264) (266)
FinancialAssetLiabilitiesNetFairValueDisclosure1 (166) (246)
Commonwealth Edison Co [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Commonwealth Edison Co [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Commonwealth Edison Co [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [8] 98 20
FinancialAssetsFairValueDisclosure1 98 20
Derivative Liability [9] 0 0
Deferred Compensation Liability, Current and Noncurrent 0 0
Financial Liabilities Fair Value Disclosure 0 0
FinancialAssetLiabilitiesNetFairValueDisclosure1 98 20
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [8] 0 0
FinancialAssetsFairValueDisclosure1 0 0
Derivative Liability [9] 0 0
Deferred Compensation Liability, Current and Noncurrent (8) (8)
Financial Liabilities Fair Value Disclosure (8) (8)
FinancialAssetLiabilitiesNetFairValueDisclosure1 (8) (8)
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability, Current (21) (19)
Derivative Liability, Noncurrent (235) (239)
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [8] 0 0
FinancialAssetsFairValueDisclosure1 0 0
Derivative Liability [9] (256) (258)
Deferred Compensation Liability, Current and Noncurrent 0 0
Financial Liabilities Fair Value Disclosure (256) (258)
FinancialAssetLiabilitiesNetFairValueDisclosure1 (256) (258)
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
PECO Energy Co [Member] | Cash and Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 47 22
PECO Energy Co [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [8] 228 45
FinancialAssetsFairValueDisclosure1 245 62
Derivative Liability 0 0
Deferred Compensation Liability, Current and Noncurrent (11) (11)
Financial Liabilities Fair Value Disclosure (11) (11)
FinancialAssetLiabilitiesNetFairValueDisclosure1 234 51
PECO Energy Co [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 17 17
PECO Energy Co [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 7 7
PECO Energy Co [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 10 10
PECO Energy Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [8] 228 45
FinancialAssetsFairValueDisclosure1 235 52
Derivative Liability 0 0
Deferred Compensation Liability, Current and Noncurrent 0 0
Financial Liabilities Fair Value Disclosure 0 0
FinancialAssetLiabilitiesNetFairValueDisclosure1 235 52
PECO Energy Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 7 7
PECO Energy Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 7 7
PECO Energy Co [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
PECO Energy Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [8] 0 0
FinancialAssetsFairValueDisclosure1 10 10
Derivative Liability 0 0
Deferred Compensation Liability, Current and Noncurrent (11) (11)
Financial Liabilities Fair Value Disclosure (11) (11)
FinancialAssetLiabilitiesNetFairValueDisclosure1 (1) (1)
PECO Energy Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 10 10
PECO Energy Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
PECO Energy Co [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 10 10
PECO Energy Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [8] 0 0
FinancialAssetsFairValueDisclosure1 0 0
Derivative Liability 0 0
Deferred Compensation Liability, Current and Noncurrent 0 0
Financial Liabilities Fair Value Disclosure 0 0
FinancialAssetLiabilitiesNetFairValueDisclosure1 0 0
PECO Energy Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
PECO Energy Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
PECO Energy Co [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Baltimore Gas and Electric Company [Member] | Cash and Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 17 13
Baltimore Gas and Electric Company [Member] | Restricted cash member [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 1  
Baltimore Gas and Electric Company [Member] | Other assets    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure   2
Baltimore Gas and Electric Company [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [8] 0 36
FinancialAssetsFairValueDisclosure1 6 40
Derivative Liability 0 0
Deferred Compensation Liability, Current and Noncurrent (5) (4)
Financial Liabilities Fair Value Disclosure (5) (4)
FinancialAssetLiabilitiesNetFairValueDisclosure1 1 36
Baltimore Gas and Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 6 4
Baltimore Gas and Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 6 4
Baltimore Gas and Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [8] 0 36
FinancialAssetsFairValueDisclosure1 6 40
Derivative Liability 0 0
Deferred Compensation Liability, Current and Noncurrent 0 0
Financial Liabilities Fair Value Disclosure 0 0
FinancialAssetLiabilitiesNetFairValueDisclosure1 6 40
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 6 4
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 6 4
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [8] 0 0
FinancialAssetsFairValueDisclosure1 0 0
Derivative Liability 0 0
Deferred Compensation Liability, Current and Noncurrent (5) (4)
Financial Liabilities Fair Value Disclosure (5) (4)
FinancialAssetLiabilitiesNetFairValueDisclosure1 (5) (4)
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [8] 0 0
FinancialAssetsFairValueDisclosure1 0 0
Derivative Liability 0 0
Deferred Compensation Liability, Current and Noncurrent 0 0
Financial Liabilities Fair Value Disclosure 0 0
FinancialAssetLiabilitiesNetFairValueDisclosure1 0 0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mutual Fund [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Pepco Holdings LLC [Member] | Successor [Member] | Cash and Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 12 19
Pepco Holdings LLC [Member] | Successor [Member] | Other assets    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 23 23
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [10] 83 217
Derivative Asset [11] 0 2
Collateral Amount Offset Against Fair Value Of Derivative Current Asset 0 (2)
Derivative assets, fair value 0 0
FinancialAssetsFairValueDisclosure1 212 348
Derivative Liability 0 0
Deferred Compensation Liability, Current and Noncurrent (25) (28)
Financial Liabilities Fair Value Disclosure (25) (28)
FinancialAssetLiabilitiesNetFairValueDisclosure1 187 320
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability [11] (1) 0
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 1 0
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 129 131
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 72 73
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 12 16
Pepco Holdings LLC [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 45 42
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [10] 83 217
Derivative Asset [11] 0 2
Collateral Amount Offset Against Fair Value Of Derivative Current Asset 0 (2)
Derivative assets, fair value 0 0
FinancialAssetsFairValueDisclosure1 155 290
Derivative Liability 0 0
Deferred Compensation Liability, Current and Noncurrent 0 0
Financial Liabilities Fair Value Disclosure 0 0
FinancialAssetLiabilitiesNetFairValueDisclosure1 155 290
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability [11] (1) 0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 1 0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 72 73
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 72 73
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [10] 0 0
Derivative Asset [11] 0 0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset 0 0
Derivative assets, fair value 0 0
FinancialAssetsFairValueDisclosure1 35 38
Derivative Liability 0 0
Deferred Compensation Liability, Current and Noncurrent (25) (28)
Financial Liabilities Fair Value Disclosure (25) (28)
FinancialAssetLiabilitiesNetFairValueDisclosure1 10 10
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability [11] 0 0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0 0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 35 38
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 12 16
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 23 22
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [10] 0 0
Derivative Asset [11] 0 0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset 0 0
Derivative assets, fair value 0 0
FinancialAssetsFairValueDisclosure1 22 20
Derivative Liability 0 0
Deferred Compensation Liability, Current and Noncurrent 0 0
Financial Liabilities Fair Value Disclosure 0 0
FinancialAssetLiabilitiesNetFairValueDisclosure1 22 20
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability [11] 0 0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0 0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 22 20
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Successor [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 22 20
Potomac Electric Power Company [Member] | Cash and Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 4 9
Potomac Electric Power Company [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [10] 36 33
Derivative Asset   0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset   0
Derivative assets, fair value   0
FinancialAssetsFairValueDisclosure1 137 133
Derivative Liability 0  
Deferred Compensation Liability, Current and Noncurrent (4) (5)
Financial Liabilities Fair Value Disclosure (4) (5)
FinancialAssetLiabilitiesNetFairValueDisclosure1 133 128
Potomac Electric Power Company [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0  
Potomac Electric Power Company [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0  
Potomac Electric Power Company [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 101 100
Potomac Electric Power Company [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 44 43
Potomac Electric Power Company [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 12 16
Potomac Electric Power Company [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 45 41
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [10] 36 33
Derivative Asset   0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset   0
Derivative assets, fair value   0
FinancialAssetsFairValueDisclosure1 80 76
Derivative Liability 0  
Deferred Compensation Liability, Current and Noncurrent 0 0
Financial Liabilities Fair Value Disclosure 0 0
FinancialAssetLiabilitiesNetFairValueDisclosure1 80 76
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0  
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0  
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 44 43
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 44 43
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [10] 0 0
Derivative Asset   0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset   0
Derivative assets, fair value   0
FinancialAssetsFairValueDisclosure1 35 38
Derivative Liability 0  
Deferred Compensation Liability, Current and Noncurrent (4) (5)
Financial Liabilities Fair Value Disclosure (4) (5)
FinancialAssetLiabilitiesNetFairValueDisclosure1 31 33
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0  
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0  
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 35 38
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 12 16
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 23 22
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [10] 0 0
Derivative Asset   0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset   0
Derivative assets, fair value   0
FinancialAssetsFairValueDisclosure1 22 19
Derivative Liability 0  
Deferred Compensation Liability, Current and Noncurrent 0 0
Financial Liabilities Fair Value Disclosure 0 0
FinancialAssetLiabilitiesNetFairValueDisclosure1 22 19
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0  
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0  
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 22 19
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 22 19
Delmarva Power and Light Company [Member] | Cash and Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 2 4
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [10] 0 42
Derivative Asset [11]   2
Collateral Amount Offset Against Fair Value Of Derivative Current Asset   (2)
Derivative assets, fair value   0
FinancialAssetsFairValueDisclosure1 0 42
Derivative Liability 0  
Deferred Compensation Liability, Current and Noncurrent (1) (1)
Financial Liabilities Fair Value Disclosure (1) (1)
FinancialAssetLiabilitiesNetFairValueDisclosure1 (1) 41
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability [10] (1)  
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 1  
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Delmarva Power and Light Company [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [10] 0 42
Derivative Asset [11]   2
Collateral Amount Offset Against Fair Value Of Derivative Current Asset   (2)
Derivative assets, fair value   0
FinancialAssetsFairValueDisclosure1 0 42
Derivative Liability 0  
Deferred Compensation Liability, Current and Noncurrent 0 0
Financial Liabilities Fair Value Disclosure 0 0
FinancialAssetLiabilitiesNetFairValueDisclosure1 0 42
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability [10] (1)  
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 1  
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [10] 0 0
Derivative Asset [11]   0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset   0
Derivative assets, fair value   0
FinancialAssetsFairValueDisclosure1 0 0
Derivative Liability 0  
Deferred Compensation Liability, Current and Noncurrent (1) (1)
Financial Liabilities Fair Value Disclosure (1) (1)
FinancialAssetLiabilitiesNetFairValueDisclosure1 (1) (1)
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability [10] 0  
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0  
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [10] 0 0
Derivative Asset [11]   0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset   0
Derivative assets, fair value   0
FinancialAssetsFairValueDisclosure1 0 0
Derivative Liability 0  
Deferred Compensation Liability, Current and Noncurrent 0 0
Financial Liabilities Fair Value Disclosure 0 0
FinancialAssetLiabilitiesNetFairValueDisclosure1 0 0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability [10] 0  
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0  
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Atlantic City Electric Company [Member] | Cash and Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 2 3
Atlantic City Electric Company [Member] | Other assets    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 23 23
Atlantic City Electric Company [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [10] 29 130
Derivative Asset   0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset   0
Derivative assets, fair value   0
FinancialAssetsFairValueDisclosure1 29 130
Derivative Liability 0  
Deferred Compensation Liability, Current and Noncurrent 0 0
Financial Liabilities Fair Value Disclosure 0 0
FinancialAssetLiabilitiesNetFairValueDisclosure1 29 130
Atlantic City Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0  
Atlantic City Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0  
Atlantic City Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Atlantic City Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Atlantic City Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Atlantic City Electric Company [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [10] 29 130
Derivative Asset   0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset   0
Derivative assets, fair value   0
FinancialAssetsFairValueDisclosure1 29 130
Derivative Liability 0  
Deferred Compensation Liability, Current and Noncurrent 0 0
Financial Liabilities Fair Value Disclosure 0 0
FinancialAssetLiabilitiesNetFairValueDisclosure1 29 130
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0  
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0  
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [10] 0 0
Derivative Asset   0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset   0
Derivative assets, fair value   0
FinancialAssetsFairValueDisclosure1 0 0
Derivative Liability 0  
Deferred Compensation Liability, Current and Noncurrent 0 0
Financial Liabilities Fair Value Disclosure 0 0
FinancialAssetLiabilitiesNetFairValueDisclosure1 0 0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0  
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0  
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure [10] 0 0
Derivative Asset   0
Collateral Amount Offset Against Fair Value Of Derivative Current Asset   0
Derivative assets, fair value   0
FinancialAssetsFairValueDisclosure1 0 0
Derivative Liability 0  
Deferred Compensation Liability, Current and Noncurrent 0 0
Financial Liabilities Fair Value Disclosure 0 0
FinancialAssetLiabilitiesNetFairValueDisclosure1 0 0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Economic Hedging Instrument Liabilites [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0  
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Effects of Netting and Allocation of Collateral Liabilities [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Derivative Liability 0  
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Rabbi Trust Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Income Investments [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure 0 0
Atlantic City Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | 6311 Life Insurance [Member]    
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]    
Investments, Fair Value Disclosure $ 0 $ 0
[1] Generation excludes cash of $259 million and $252 million at December 31, 2017 and 2016 and restricted cash of $127 million and $157 million at December 31, 2017 and 2016. Exelon excludes cash of $389 million and $360 million at December 31, 2017 and 2016 and restricted cash of $145 million and $180 million at December 31, 2017 and 2016 and includes long-term restricted cash of $85 million and $25 million at December 31, 2017 and 2016, which is reported in Other deferred debits on the Consolidated Balance Sheets.
[2] Collateral posted/(received) from counterparties totaled $65 million, $320 million and $81 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2017. Collateral posted/(received) from counterparties totaled $71 million, $197 million and $61 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2016.
[3] Of the collateral posted/(received), $(117) million and $(158) million represents variation margin on the exchanges as of December 31, 2017 and 2016, respectively.
[4] Excludes net liabilities of $82 million and $31 million at December 31, 2017 and 2016, respectively. These items consist of receivables related to pending securities sales, interest and dividend receivables, repurchase agreement obligations, and payables related to pending securities purchases. The repurchase agreements are generally short-term in nature with durations generally of 30 days or less.
[5] Includes $77 million and $29 million of cash received from outstanding repurchase agreements at December 31, 2017 and 2016, respectively, and is offset by an obligation to repay upon settlement of the agreement as discussed in (d) below.
[6] Includes derivative instruments of less than $1 million and $(2) million, which have a total notional amount of $811 million and $933 million at December 31, 2017 and 2016, respectively. The notional principal amounts for these instruments provide one measure of the transaction volume outstanding as of the fiscal years ended and do not represent the amount of the company's exposure to credit or market loss.
[7] Amount represents the net fair value of out-of-the-money derivative contracts containing credit-risk related contingent features after considering the mitigating effects of offsetting positions under master netting arrangements and reflects the actual net liability upon which any potential contingent collateral obligations would be based.
[8] ComEd excludes cash of $45 million and $36 million at December 31, 2017 and 2016 and restricted cash of $2 million at December 31, 2016 and includes long-term restricted cash of $62 million at December 31, 2017, which is reported in Other deferred debits on the Consolidated Balance Sheets. PECO excludes cash of $47 million and $22 million at December 31, 2017 and 2016. BGE excludes cash of $17 million and $13 million at December 31, 2017 and 2016 and restricted cash of $1 million at December 31, 2017 and includes long-term restricted cash of $2 million at December 31, 2016, which is reported in Other deferred debits on the Consolidated Balance Sheets.
[9] The Level 3 balance consists of the current and noncurrent liability of $21 million and $235 million, respectively, at December 31, 2017, and $19 million and $239 million, respectively, at December 31, 2016, related to floating-to-fixed energy swap contracts with unaffiliated suppliers.
[10] PHI excludes cash of $12 million and $19 million at December 31, 2017 and 2016 and includes long term restricted cash of $23 million at both December 31, 2017 and 2016 which is reported in Other deferred debits on the Consolidated Balance Sheets. Pepco excludes cash of $4 million and $9 million at December 31, 2017 and 2016. DPL excludes cash of $2 million and $4 million at December 31, 2017 and 2016. ACE excludes cash of $2 million and $3 million at December 31, 2017 and 2016 and includes long-term restricted cash of $23 million at both December 31, 2017 and 2016 which is reported in Other deferred debits on the Consolidated Balance Sheets.
[11] Represents natural gas futures purchased by DPL as part of a natural gas hedging program approved by the DPSC.