Derivative Financial Instruments - Narrative (Details) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) MWh		Sep. 30, 2014 USD ($) MWh	Jun. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Derivative [Line Items]
Income taxes		$ 115	$ 422	$ 805		$ 646
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax			28	$ 2		130
Hypothetical Increase In Interest Rates				0.50%
Mark-to-market derivative assets (noncurrent assets)		801		$ 801				$ 773
Hypothetical increase in interest rates associated with variable-rate debt				3
Ineffective portion recognized in income		3	6	11	[1]	14
Mark-to-market derivative liabilities (noncurrent liabilities)		360		360				403
Cash collateral held		13		13
Letters of credit collateral posted		25		25
Interest Rate Fair Value Hedge Asset at Fair Value		40		40
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount of Pre-issuance Interest Rate Cash Flow Hedge Derivatives		752		752
ReNewAble Energy Contract [Member]
Derivative [Line Items]
Derivative Asset, Fair Value of Collateral		19		19
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Income taxes		(36)	291	$ 371		$ 290
Proprietary trading activities volume | MWh				3,006,000		8,129,000
Mark-to-market derivative assets (noncurrent assets)		764		$ 764				771
Mark-to-market derivative liabilities (noncurrent liabilities)		139		139				105
Cash collateral received not offset against net derivative positions		4		4				8
Credit exposure under natural gas supply and management agreements		2,106		2,106
Cash collateral posted		1,065		1,065				1,497
Letters of credit collateral posted		474		474				672
Cash collateral held		21		21				77
Letters of credit collateral posted		40		40				24
Incremental collateral for loss of investment grade credit rating		2,100		2,100				2,400
Interest Rate Fair Value Hedge Asset at Fair Value		3		3
Commonwealth Edison Co [Member]
Derivative [Line Items]
Income taxes		99	84	226		$ 221
Mark-to-market derivative liabilities (noncurrent liabilities)		221		221				187
PECO Energy Co [Member]
Derivative [Line Items]
Income taxes		37	25	$ 122		82
Estimated percentage of natural gas purchases hedged				30.00%
Incremental collateral for loss of investment grade credit rating		18		$ 18
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Income taxes		35	31	141		103
Total		1		1
Incremental collateral for loss of investment grade credit rating		28		$ 28
Minimum [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected Generation Hedged In Next Twelve Months				97.00%
Expected Generation Hedged In Year Two				81.00%
Expected generation hedged in year three				51.00%
Minimum [Member] | Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged				10.00%
Maximum [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected Generation Hedged In Next Twelve Months				100.00%
Expected Generation Hedged In Year Two				84.00%
Expected generation hedged in year three				54.00%
Maximum [Member] | Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged				20.00%
Interest Rate Swap [Member] | Derivative [Member]
Derivative [Line Items]
Derivative, Notional Amount		800		$ 800
Interest Rate Swap [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities (noncurrent liabilities)		4		4
Foreign Exchange Contract [Member] | Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount		99		99
Fair Value Hedging [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount		800		800				1,450
Derivative, Gain (Loss) on Derivative, Net		16	(8)
Mark-to-market derivative assets (noncurrent assets)		37		37				29
Fair Value Hedging [Member] | Interest Rate Swap [Member] | Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount								550
Derivative, Gain (Loss) on Derivative, Net	[1]	0	(4)
Mark-to-market derivative assets (noncurrent assets)								7
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount of Pre-issuance Interest Rate Cash Flow Hedge Derivatives								$ 400
Other Solar Projects [Member] | Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional amounts on forward starting interest rate swaps		25		25
Mark-to-market derivative liabilities (noncurrent liabilities)		3		3
Other Solar Projects [Member] | Cash Flow Hedging [Member] | Interest Rate Swap [Member] | Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount		26		26
PHI Merger [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Gain (Loss) on Derivative, Net				64
PHI Merger [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount							$ 2,400
ExGen Texas Power [Member] | Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount		501		501
ExGen Texas Power [Member] | Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Mark-to-market derivative liabilities (noncurrent liabilities)		16		16
ExGen Texas Power [Member] | Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Notional Amount		200		200
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax				26
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Derivative [Line Items]
Income taxes	[2]	(1)	12	(13)		52
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Income taxes	[2]	(1)	$ 12	(3)		$ 52
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility		24		24
PECO Energy Co Affiliate [Member] | PECO Energy Co [Member]
Derivative [Line Items]
Net receivable from affiliated electric and gas utility		33		33
Baltimore Gas And Electric Company Affiliate [Member] | Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Net receivable from affiliated electric and gas utility		$ 27		$ 27

[1] For the three and nine months ended September 30, 2015, the loss on Generation swaps included $0 million and $1 million realized in earnings, respectively, with an immaterial amount excluded from hedge effectiveness testing. For the three and nine months ended September 30, 2014, the loss on Generation swaps included $4 million and $12 million realized in earnings, respectively, with an $2 million amount excluded from hedge effectiveness testing.

[2] All amounts are net of tax. Amounts in parentheses represent a decrease in net income.