Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015		Sep. 30, 2014
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]			$ (2,684)		$ (2,040)
OCI before reclassifications	[1]			(64)		229
Amounts reclassified from AOCI	[1],[2]			152		(106)
Net current-period OCI		$ 32	$ (11)	88	[1]	123	[1]
Ending balance	[1]	(2,596)	(1,917)	(2,596)		(1,917)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]			(28)		120
OCI before reclassifications	[1]			(18)		(14)
Amounts reclassified from AOCI	[1],[2]			22		(78)
Net current-period OCI	[1]			4		(92)
Ending balance	[1]	(24)	28	(24)		28
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance				3	[1]	2
OCI before reclassifications	[1]			0		(2)
Net current-period OCI	[1]			0		(2)
Ending balance	[1]	3	0	3		0
Accumulated Defined Benefit Plans Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]			(2,640)		(2,260)
OCI before reclassifications	[1]			(29)		240
Amounts reclassified from AOCI	[1],[2]			130		91
Net current-period OCI	[1]			101		331
Ending balance	[1]	(2,539)	(1,929)	(2,539)		(1,929)
Accumulated Translation Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance				(19)	[1]	(10)
OCI before reclassifications	[1]			(17)		(6)
Net current-period OCI	[1]			(17)		(6)
Ending balance	[1]	(36)	(16)	(36)		(16)
Accumulated Equity Investment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]			0		108
OCI before reclassifications	[1]			0		11
Amounts reclassified from AOCI	[1],[2]			0		(119)
Net current-period OCI	[1]			0		(108)
Ending balance	[1]	0	0	0		0
Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]			(36)		214
OCI before reclassifications	[1]			(30)		(6)
Amounts reclassified from AOCI	[1],[2]			6		(197)
Net current-period OCI		(13)	(26)	(24)	[1]	(203)	[1]
Ending balance	[1]	(60)	11	(60)		11
Exelon Generation Co L L C [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]			(18)		114
OCI before reclassifications	[1]			(13)		(8)
Amounts reclassified from AOCI	[1],[2]			6		(78)
Net current-period OCI	[1]			(7)		(86)
Ending balance	[1]	(25)	28	(25)		28
Exelon Generation Co L L C [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]			1		2
OCI before reclassifications	[1]			0		(3)
Net current-period OCI	[1]			0		(3)
Ending balance	[1]	1	(1)	1		(1)
Exelon Generation Co L L C [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]					0
Ending balance	[1]		0			0
Exelon Generation Co L L C [Member] | Accumulated Translation Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance				(19)	[1]	(10)
OCI before reclassifications	[1]			(17)		(6)
Net current-period OCI	[1]			(17)		(6)
Ending balance	[1]	(36)	(16)	(36)		(16)
Exelon Generation Co L L C [Member] | Accumulated Equity Investment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]			0		108
OCI before reclassifications	[1]			0		11
Amounts reclassified from AOCI	[1],[2]			0		(119)
Net current-period OCI	[1]			0		(108)
Ending balance	[1]	0	0	0		0
PECO Energy Co [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]			1		1
Ending balance	[1]	1	1	1		1
PECO Energy Co [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]			0		0
Ending balance	[1]	0	0	0		0
PECO Energy Co [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]			1		1
Ending balance	[1]	$ 1	$ 1	$ 1		$ 1

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

[2] See tables following changes in accumulated other comprehensive income tables for details about these reclassifications.