Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	$ (2,040)	[1]	$ (2,767)	[1]
OCI before reclassifications	(528)		791	[1]
Amounts reclassified from AOCI	(116)		(64)	[1],[2]
Other comprehensive income (loss)	(644)		727	[1]	(317)
Ending balance	(2,684)		(2,040)	[1]	(2,767)	[1]
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	120	[1]	368	[1]
OCI before reclassifications	(31)		29	[1]
Amounts reclassified from AOCI	(117)		(277)	[1],[2]
Other comprehensive income (loss)	(148)		(248)	[1]
Ending balance	(28)		120	[1]
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	2	[1]
OCI before reclassifications	(1)		2	[1]
Amounts reclassified from AOCI	2
Other comprehensive income (loss)	1		2	[1]
Ending balance	3		2	[1]
Accumulated Defined Benefit Plans Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(2,260)	[1]	(3,137)	[1]
OCI before reclassifications	(498)		669	[1]
Amounts reclassified from AOCI	118		208	[1],[2]
Other comprehensive income (loss)	(380)		877	[1]
Ending balance	(2,640)		(2,260)	[1]
Accumulated Translation Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(10)	[1]
OCI before reclassifications	(9)		(10)	[1]
Other comprehensive income (loss)	(9)		(10)	[1]
Ending balance	(19)		(10)	[1]
Accumulated Equity Investment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	108	[1]	2	[1]
OCI before reclassifications	11		101	[1]
Amounts reclassified from AOCI	(119)		5	[1],[2]
Other comprehensive income (loss)	(108)		106	[1]
Ending balance	0		108	[1]
Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	214	[1]	513	[1]
OCI before reclassifications	(14)		109	[1]
Amounts reclassified from AOCI	(236)		(408)	[1],[2]
Other comprehensive income (loss)	(250)		(299)	[1]	(402)
Ending balance	(36)		214	[1]	513	[1]
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	114	[1]	512	[1]
OCI before reclassifications	(15)		15	[1]
Amounts reclassified from AOCI	(117)		(413)	[1],[2]
Other comprehensive income (loss)	(132)		(398)	[1]
Ending balance	(18)		114	[1]
Exelon Generation Co L L C [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	2	[1]	0	[1]
OCI before reclassifications	(1)		2	[1]
Other comprehensive income (loss)	(1)		2	[1]
Ending balance	1		2	[1]
Exelon Generation Co L L C [Member] | Accumulated Translation Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(10)	[1]
OCI before reclassifications	(9)		(10)	[1]
Other comprehensive income (loss)	(9)		(10)	[1]
Ending balance	(19)		(10)	[1]
Exelon Generation Co L L C [Member] | Accumulated Equity Investment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	108	[1]	1	[1]
OCI before reclassifications	11		102	[1]
Amounts reclassified from AOCI	(119)		5	[1],[2]
Other comprehensive income (loss)	(108)		107	[1]
Ending balance	0		108	[1]
PECO Energy Co [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	1	[1]	1	[1]
Other comprehensive income (loss)	0		0		1
Ending balance	1		1	[1]	1	[1]
PECO Energy Co [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Ending balance	$ 1		$ 1	[1]	$ 1	[1]

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

[2] See next tables for details about these reclassifications.