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Fair Value of Financial Assets and Liabilities - Fair Value Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation (Details) - USD ($)
 3 Months Ended 6 Months Ended 9 Months Ended
Sep. 30, 2016
Mar. 23, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2016
Sep. 30, 2015
Jun. 30, 2016
Mar. 24, 2016
Dec. 31, 2015
Jun. 30, 2015
Dec. 31, 2014
Fair Value, Inputs, Level 3 [Member]                      
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value $ 1,466,000,000   $ 1,661,000,000 $ 1,466,000,000 $ 1,466,000,000 $ 1,661,000,000 $ 1,185,000,000 $ 20,000,000 $ 1,529,000,000 $ 1,536,000,000 $ 1,501,000,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings 93,000,000   (48,000,000)   (334,000,000) (83,000,000)          
Total realized / unrealized gains (losses)                      
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates 0   0   0 0          
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable (1,000,000)   1,000,000   1,000,000 2,000,000          
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets (17,000,000)   (20,000,000)   21,000,000 (19,000,000)          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases 214,000,000   67,000,000   420,000,000 259,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales (7,000,000)   (18,000,000)   (11,000,000) (42,000,000)          
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) 288,000,000   180,000,000   248,000,000 538,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances 0       (1,000,000)            
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements (28,000,000)   (13,000,000)   (119,000,000) (75,000,000)          
Purchases, sales, issuances and settlements                      
Purchases 214,000,000   67,000,000   420,000,000 259,000,000          
Ending balance                
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]                      
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Change In Collateral 31,000,000   90,000,000   (51,000,000) 72,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 0   69,000,000   2,000,000 84,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 (4,000,000)   (3,000,000)   (11,000,000) (38,000,000)          
Fair Value, Inputs, Level 3 [Member] | Consolidation, Eliminations [Member]                      
Total realized / unrealized gains (losses)                      
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates (6,000,000)   0   (18,000,000) (17,000,000)          
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets 6,000,000   0   18,000,000 17,000,000          
Exelon Generation Co L L C [Member]                      
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]                      
Fair Value, Assets and Liabilities Measured on Recurring Basis, Gain (Loss) Included in Earnings 190,000,000   229,000,000   579,000,000 623,000,000          
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member]                      
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]                      
Realized Investment Gains (Losses) 2,000,000   1,000,000   13,000,000 8,000,000          
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member]                      
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value 1,689,000,000   1,904,000,000 1,689,000,000 1,689,000,000 1,904,000,000 1,386,000,000   1,776,000,000 1,759,000,000 1,708,000,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings 92,000,000   (48,000,000)   (336,000,000) (83,000,000)          
Total realized / unrealized gains (losses)                      
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates 6,000,000   0   18,000,000 17,000,000          
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable (1,000,000)   1,000,000   1,000,000 2,000,000          
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets 0   0   0 0          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases 214,000,000   67,000,000   420,000,000 259,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales (7,000,000)   (18,000,000)   (11,000,000) (42,000,000)          
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) 288,000,000   180,000,000   247,000,000 538,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements (28,000,000)   (13,000,000)   (119,000,000) (75,000,000)          
Purchases, sales, issuances and settlements                      
Purchases 214,000,000   67,000,000   420,000,000 259,000,000          
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]                      
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Period Increase (Decrease) 25,000,000   19,000,000   10,000,000 44,000,000          
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Change In Collateral 31,000,000   90,000,000   (51,000,000) 72,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 0   69,000,000   2,000,000 84,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 (4,000,000)   (3,000,000)   (11,000,000) (38,000,000)          
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]                      
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value 693,000,000   669,000,000 693,000,000 693,000,000 669,000,000 715,000,000   670,000,000 667,000,000 605,000,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings (4,000,000)   0   2,000,000 4,000,000          
Total realized / unrealized gains (losses)                      
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates 6,000,000   0   18,000,000 17,000,000          
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable 0   0   0 0          
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets     0     0          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases 4,000,000   15,000,000   123,000,000 122,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales 0   0   (1,000,000) (8,000,000)          
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) 3,000,000   (1,000,000)   7,000,000 2,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements (28,000,000)   (13,000,000)   (119,000,000) (75,000,000)          
Purchases, sales, issuances and settlements                      
Purchases 4,000,000   15,000,000   123,000,000 122,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3     0     0          
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]                      
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Change In Collateral 0   0   0 0          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 0   0   0 4,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 0       0            
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Pledged Assets For Zion Station Decommissioning [Member]                      
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value 19,000,000   29,000,000 19,000,000 19,000,000 29,000,000 25,000,000   22,000,000 41,000,000 50,000,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings 0   0   0 0          
Total realized / unrealized gains (losses)                      
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates 0   0   0 0          
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable (1,000,000)   1,000,000   1,000,000 2,000,000          
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets     0     0          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases 0   0   1,000,000 1,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales (5,000,000)   (13,000,000)   (5,000,000) (24,000,000)          
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) 0       0 0          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements 0   0   0 0          
Purchases, sales, issuances and settlements                      
Purchases 0   0   1,000,000 1,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3     0     0          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3     0     0          
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]                      
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Change In Collateral 0   0   0 0          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 0       0            
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 0       0            
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]                      
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value 935,000,000   1,174,000,000 935,000,000 935,000,000 1,174,000,000 609,000,000   1,051,000,000 1,021,000,000 1,050,000,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings 95,000,000 [1]   (48,000,000) [2]   (339,000,000) [1] (87,000,000) [2]          
Total realized / unrealized gains (losses)                      
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates 0   0   0 0          
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable 0   0   0 0          
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets     0     0          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases 207,000,000 [3]   50,000,000   289,000,000 [3] 107,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales (2,000,000)   (5,000,000)   (5,000,000) (10,000,000)          
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) 285,000,000   181,000,000   240,000,000 536,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements 0   0   0 0          
Purchases, sales, issuances and settlements                      
Purchases 207,000,000 [3]   50,000,000   289,000,000 [3] 107,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3     (3,000,000)                
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]                      
Indefinite-lived Intangible Assets Acquired         168,000,000            
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Change In Collateral 31,000,000   90,000,000   (51,000,000) 72,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 (1,000,000)   69,000,000   1,000,000 80,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 (4,000,000)       (11,000,000) (38,000,000)          
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Other Investments [Member]                      
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value 42,000,000   32,000,000 42,000,000 42,000,000 32,000,000 37,000,000   33,000,000 30,000,000 3,000,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings 1,000,000   0   1,000,000 0          
Total realized / unrealized gains (losses)                      
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates 0   0   0 0          
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable 0   0   0 0          
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets     0     0          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases 3,000,000   2,000,000   7,000,000 29,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales 0   0   0 0          
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) 0       0 0          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements 0   0   0 0          
Purchases, sales, issuances and settlements                      
Purchases 3,000,000   2,000,000   7,000,000 29,000,000          
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]                      
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Change In Collateral 0   0   0 0          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 1,000,000   0   1,000,000 0          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 0   0   0 0          
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]                      
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value (244,000,000) [4]   (243,000,000) [5] (244,000,000) [4] (244,000,000) [4] (243,000,000) [5] (221,000,000) [4]   (247,000,000) [4] (223,000,000) [5] (207,000,000) [5]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings 0 [4]   0 [5]   0 [4] 0 [5]          
Total realized / unrealized gains (losses)                      
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates 0 [4]   0 [5]   0 [4] 0 [5]          
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable 0 [4]   0 [5]   0 [4] 0 [5]          
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets (23,000,000) [4]   (20,000,000) [5]   3,000,000 [4] (36,000,000) [5]          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases 0 [4]   0 [5]   0 [4] 0 [5]          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales 0 [4]   0 [5]   0 [4] 0 [5]          
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) 0 [4]       0 [4] 0 [5]          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements 0 [4]   0 [5]   0 [4] 0 [5]          
Purchases, sales, issuances and settlements                      
Purchases 0 [4]   0 [5]   0 [4] 0 [5]          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3 [5]     0     0          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3 [5]     0     0          
Ending balance [5]     (243,000,000)     (243,000,000)          
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]                      
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Change In Collateral 0 [4]   0 [5]   0 [4] 0 [5]          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 [4] 0       0            
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 [4] 0       0            
Pepco Holdings LLC [Member] | 6311 Life Insurance [Member] | Predecessor [Member]                      
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings   $ 0                  
Pepco Holdings LLC [Member] | 6311 Life Insurance [Member] | Successor [Member]                      
Total realized / unrealized gains (losses)                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases       (1,000,000)              
Purchases, sales, issuances and settlements                      
Purchases       (1,000,000)              
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Predecessor [Member]                      
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings     16,000,000                
Total realized / unrealized gains (losses)                      
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)     15,000,000                
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Successor [Member]                      
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value               20,000,000      
Total realized / unrealized gains (losses)                      
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) 0                    
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | 6311 Life Insurance [Member]                      
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings       (2,000,000)              
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | 6311 Life Insurance [Member] | Predecessor [Member]                      
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value   20,000,000 19,000,000     19,000,000     19,000,000 20,000,000 19,000,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings   1,000,000 1,000,000     4,000,000          
Total realized / unrealized gains (losses)                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases   0 (2,000,000)     (3,000,000)          
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)   1,000,000 0     2,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements           (1,000,000)          
Purchases, sales, issuances and settlements                      
Purchases   0 (2,000,000)     (3,000,000)          
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | 6311 Life Insurance [Member] | Successor [Member]                      
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value 21,000,000     21,000,000 21,000,000   20,000,000 $ 20,000,000      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings 1,000,000                    
Total realized / unrealized gains (losses)                      
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates 0     0              
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Nuclear Decommissioning Payable 0     0              
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Regulatory assets 0     0              
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases 0     0              
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales 0     0              
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) 0     1,000,000              
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Issuances 0     (1,000,000)              
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements 0   0 0              
Purchases, sales, issuances and settlements                      
Purchases 0     0              
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3 0     0              
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3 0     0              
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]                      
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Change In Collateral 0     0              
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Preferred Stock [Member] | Predecessor [Member]                      
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value   0 18,000,000     18,000,000     18,000,000 3,000,000 3,000,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings   (18,000,000) 15,000,000     15,000,000          
Total realized / unrealized gains (losses)                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases   0 0     0          
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)   0       15,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements   0 0     0          
Purchases, sales, issuances and settlements                      
Purchases   $ 0 0     0          
Pepco Holdings LLC [Member] | Fair Value, Inputs, Level 3 [Member] | Preferred Stock [Member] | Successor [Member]                      
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value     18,000,000     18,000,000          
Total realized / unrealized gains (losses)                      
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)     15,000,000                
Delmarva Power and Light Company [Member] | 6311 Life Insurance [Member]                      
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings           0          
Total realized / unrealized gains (losses)                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases           0          
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)           0          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements           1,000,000          
Purchases, sales, issuances and settlements                      
Purchases           0          
Ending balance     0     0          
Delmarva Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | 6311 Life Insurance [Member]                      
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value                     1,000,000
Potomac Electric Power Company [Member] | 6311 Life Insurance [Member]                      
Total realized / unrealized gains (losses)                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases 0   (3,000,000)   (1,000,000) (4,000,000)          
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)         2,000,000 2,000,000          
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements 0   0   0 0          
Purchases, sales, issuances and settlements                      
Purchases 0   (3,000,000)   (1,000,000) (4,000,000)          
Ending balance     18,000,000     18,000,000          
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member]                      
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings 1,000,000   1,000,000                
Total realized / unrealized gains (losses)                      
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) 0   0                
Potomac Electric Power Company [Member] | Fair Value, Inputs, Level 3 [Member] | 6311 Life Insurance [Member]                      
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value $ 21,000,000   18,000,000 $ 21,000,000 21,000,000 18,000,000 $ 20,000,000   $ 19,000,000 $ 20,000,000 $ 18,000,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings     1,000,000                
Total realized / unrealized gains (losses)                      
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases         3,000,000 4,000,000          
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)     $ 0                
Purchases, sales, issuances and settlements                      
Purchases         $ 3,000,000 $ 4,000,000          
[1] Includes a reduction for the reclassification of $190 million and $579 million of realized gains due to the settlement of derivative contracts recorded in results of operations for the three and nine months ended September 30, 2016, respectively.
[2] Includes a reduction for the reclassification of $229 million and $623 million of realized gains due to the settlement of derivative contracts recorded in results of operations for the three and nine months ended September 30, 2015, respectively.
[3] Includes $168 million of fair value from contracts acquired as a result of portfolio acquisitions.
[4] Includes $25 million of decreases in fair value and realized losses due to settlements of $2 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the three months ended September 30, 2016. Includes $10 million of decreases in fair value and realized losses due to settlements of $13 million for the nine months ended September 30, 2016.
[5] ncludes $19 million of decreases in fair value and a reduction for realized gains due to settlements of $1 million recorded in purchased power expense associated with floating-to-fixed energy swap contracts with unaffiliated suppliers for the three months ended September 30, 2015. Includes $44 million of decreases in fair value and an increase for realized losses due to settlements of $8 million for the nine months ended September 30, 2015.