Derivative Financial Instruments - Summary of AOCI related to Cash Flow Hedges (Details) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
		Jun. 30, 2015		Jun. 30, 2014	Jun. 30, 2015		Jun. 30, 2014	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Gain loss on interest rate swap treasury rate lock net of tax				$ 25	$ 10		$ 40
Income taxes		$ (327)		(277)	(690)		(224)
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Income taxes		(181)		(199)	(407)		1
Electrical Generation Revenue		(4,079)		(3,588)	(9,709)		(7,644)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Derivative [Line Items]
Income taxes	[1]	0		(25)	10		(40)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Income taxes	[1]	0		(25)	0		(40)
Energy Related Hedges [Member]
Derivative [Line Items]
Effective portion of changes in fair value							(9)
Energy Related Hedges [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Cash Flow Hedge Accumulated Other Comprehensive Income Gain Loss		(21)		45	(21)		45		$ (18)		$ 116
Energy Related Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Exelon Generation Co L L C [Member] | Operating Revenue One [Member]
Derivative [Line Items]
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion					(2)		(62)
Energy Related Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Exelon Generation Co L L C [Member] | Interest Expense [Member]
Derivative [Line Items]
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion					(5)
Cash Flow Hedging [Member]
Derivative [Line Items]
Effective portion of changes in fair value		1			(10)		(11)
Cash Flow Hedging [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Cash Flow Hedge Accumulated Other Comprehensive Income Gain Loss		(19)		47	(19)		47		$ (28)		$ 120
Cash Flow Hedging [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Operating Revenue One [Member]
Derivative [Line Items]
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion					(2)		(62)
Cash Flow Hedging [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Interest Expense [Member]
Derivative [Line Items]
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion					(5)
Cash Flow Hedging [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Other, net [Member]
Derivative [Line Items]
Derivative Instruments, Gain Reclassified from Accumulated OCI into Income, Effective Portion					(16)
Total Cash Flow Hedges [Member]
Derivative [Line Items]
Cash Flow Hedge Accumulated Other Comprehensive Income Gain Loss		(19)		47	(19)		47	$ (22)		$ 95
Effective portion of changes in fair value				(10)
Total Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Operating Revenue One [Member]
Derivative [Line Items]
Electrical Generation Revenue		(2)		(38)
Energy Related Hedges [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Cash Flow Hedge Accumulated Other Comprehensive Income Gain Loss		(21)	[2]	45	(21)	[2]	$ 45	$ (23)		$ 88
Effective portion of changes in fair value		0		(5)	$ (6)
Energy Related Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Exelon Generation Co L L C [Member] | Operating Revenue One [Member]
Derivative [Line Items]
Electrical Generation Revenue		$ (2)		$ (38)

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

[2] Total Cash Flow Hedge OCI Activity, Net of Income Tax Generation Exelon Six Months Ended June 30, 2015 Income StatementLocation Total Cash FlowHedges Total Cash FlowHedges Accumulated OCI derivative gain at December 31, 2014 $(18) $(28) Effective portion of changes in fair value (6) (10) Reclassifications from accumulated OCI to net incomeOther, net — 16(a) Reclassifications from accumulated OCI to net incomeInterest Expense 5 5 Reclassifications from accumulated OCI to net incomeOperating Revenues (2) (2) Accumulated OCI derivative gain at June 30, 2015 $(21) $(19)