Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015		Jun. 30, 2014
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]			$ (2,684)		$ (2,040)
OCI before reclassifications	[1]			(48)		246
Amounts reclassified from AOCI	[1],[2]			106		(112)
Net current-period OCI		$ 50	$ 131	58	[1]	134	[1]
Ending balance	[1]	(2,626)	(1,906)	(2,626)		(1,906)
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]			(10)		(11)
Amounts reclassified from AOCI	[1],[2]			19		(62)
Net current-period OCI	[1]			9		(73)
Ending balance	[1]	(19)	47	(19)		47
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		1
Net current-period OCI	[1]			0		1
Ending balance	[1]	3	3	3		3
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)		246
Amounts reclassified from AOCI	[1],[2]			87		66
Net current-period OCI	[1]			58		312
Ending balance	[1]	(2,582)	(1,948)	(2,582)		(1,948)
Accumulated Translation Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance				(19)	[1]	(10)
OCI before reclassifications	[1]			(9)		(1)
Net current-period OCI	[1]			(9)		(1)
Ending balance	[1]	(28)	(11)	(28)		(11)
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		(116)
Net current-period OCI	[1]			0		(105)
Ending balance	[1]	0	3	0		3
Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	[1]			(36)		214
OCI before reclassifications	[1]			(14)		1
Amounts reclassified from AOCI	[1],[2]			3		(178)
Net current-period OCI		6	(155)	(11)	[1]	(177)	[1]
Ending balance	[1]	(47)	37	(47)		37
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]			(6)		(8)
Amounts reclassified from AOCI	[1],[2]			3		(62)
Net current-period OCI	[1]			(3)		(70)
Ending balance	[1]	(21)	44	(21)		44
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]			1		(1)
Net current-period OCI	[1]			1		(1)
Ending balance	[1]	2	1	2		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]			(9)		(1)
Net current-period OCI	[1]			(9)		(1)
Ending balance	[1]	(28)	(11)	(28)		(11)
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		(116)
Net current-period OCI	[1]			0		(105)
Ending balance	[1]	0	3	0		3
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.