Derivative Financial Instruments - Summary of AOCI related to Cash Flow Hedges (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended				12 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013		Dec. 31, 2013	Dec. 31, 2012
Effect of Hedges on Accumulated Other Comprehensive Income [Roll Forward]
Reclassifications from accumulated OCI to net income							$ 133
Net gain (loss) related to ineffective portion of changes in fair value of treasury rate locks							11			20
Effective Portion Of Change In Fair Value Of Treasury Rate Lock Net Of Tax	13		2		13		25		5
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	12		33		52		215
Exelon Generation Co L L C [Member]
Effect of Hedges on Accumulated Other Comprehensive Income [Roll Forward]
Reclassifications from accumulated OCI to net income	4,300		3,871		11,944		10,729
Energy Related Hedges [Member] | Exelon Generation Co L L C [Member]
Effect of Hedges on Accumulated Other Comprehensive Income [Roll Forward]
Accumulated OCI derivative gain - Beginning Balance	57		255		119		532		532
Effective portion of changes in fair value	0		0		0		0
Accumulated OCI derivative gain - Ending Balance	41	[1]	204	[2],[3]	41	[1]	204	[2],[3]
Energy Related Hedges [Member] | Operating Revenue One [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]
Effect of Hedges on Accumulated Other Comprehensive Income [Roll Forward]
Reclassifications from accumulated OCI to net income	(16)		(51)		(78)		(328)
Total Cash Flow Hedges [Member]
Effect of Hedges on Accumulated Other Comprehensive Income [Roll Forward]
Accumulated OCI derivative gain - Beginning Balance	47		245		120		368		368
Effective portion of changes in fair value	(3)		2		(14)		25
Accumulated OCI derivative gain - Ending Balance	28		199		28		199			368
Effective Portion Of Change In Fair Value Of Treasury Rate Lock Net Of Tax										(133)
Total Cash Flow Hedges [Member] | Operating Revenue One [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Effect of Hedges on Accumulated Other Comprehensive Income [Roll Forward]
Reclassifications from accumulated OCI to net income	(16)		(48)		(78)		(194)
Interest Rate Contract [Member] | Energy Related Hedges [Member] | Exelon Generation Co L L C [Member]
Effect of Hedges on Accumulated Other Comprehensive Income [Roll Forward]
Accumulated OCI derivative gain - Ending Balance			$ 11				$ 11

[1] Excludes $13 million of losses, net of taxes, related to interest rate swaps and treasury rate locks as of September 30, 2014 and June 30, 2014.

[2] Amount is net of related income tax expense of $33 million for the three months ended September 30, 2013.

[3] Excludes $11 million of losses, net of taxes, related to interest rate swaps and treasury rate locks as of September 30, 2013 and June 30, 2013