Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2013		Dec. 31, 2014
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	$ (2,684)	[1]	$ (2,040)	[1]
OCI before reclassifications	(49)	[1]	(8)	[1]
Amounts reclassified from AOCI	60	[1],[2]	12	[1],[2]
Net current-period OCI	11	[1]	4	[1]
Ending balance	(2,673)	[1]	(2,036)	[1]
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(28)	[1]	120	[1]
OCI before reclassifications	(11)	[1]	(1)	[1]
Amounts reclassified from AOCI	17	[1],[2]	(24)	[1],[2]
Net current-period OCI	6	[1]	(25)	[1]
Ending balance	(22)	[1]	95	[1]
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	3	[1]	2
OCI before reclassifications	0	[1]	0	[1]
Net current-period OCI	0	[1]	0	[1]
Ending balance	3	[1]	2	[1]
Accumulated Defined Benefit Plans Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(2,640)	[1]	(2,260)	[1]
OCI before reclassifications	(26)	[1]	(13)	[1]
Amounts reclassified from AOCI	43	[1],[2]	35	[1],[2]
Net current-period OCI	17	[1]	22	[1]
Ending balance	(2,623)	[1]	(2,238)	[1]
Accumulated Translation Adjustment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(19)	[1]	(10)
OCI before reclassifications	(12)	[1]	(5)	[1]
Net current-period OCI	(12)	[1]	(5)	[1]
Ending balance	(31)	[1]	(15)	[1]
Accumulated Equity Investment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	0	[1]	108	[1]
OCI before reclassifications	0	[1]	11	[1]
Amounts reclassified from AOCI	0	[1],[2]	1	[1],[2]
Net current-period OCI	0	[1]	12	[1]
Ending balance	0	[1]	120	[1]
Exelon Generation Co L L C [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(36)	[1]	214	[1]
OCI before reclassifications	(18)	[1]	2	[1]
Amounts reclassified from AOCI	1	[1],[2]	(23)	[1],[2]
Net current-period OCI	(17)	[1]	(21)	[1]
Ending balance	(53)	[1]	193	[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	(18)	[1]	114	[1]
OCI before reclassifications	(6)	[1]	(1)	[1]
Amounts reclassified from AOCI	1	[1],[2]	(24)	[1],[2]
Net current-period OCI	(5)	[1]	(25)	[1]
Ending balance	(23)	[1]	89	[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	1	[1]	2	[1]
OCI before reclassifications	0	[1]	(3)	[1]
Net current-period OCI	0	[1]	(3)	[1]
Ending balance	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					0	[1]
Ending balance			0	[1]	0	[1]
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	(12)	[1]	(5)	[1]
Net current-period OCI	(12)	[1]	(5)	[1]
Ending balance	(31)	[1]	(15)	[1]
Exelon Generation Co L L C [Member] | Accumulated Equity Investment [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	0	[1]	108	[1]
OCI before reclassifications	0	[1]	11	[1]
Amounts reclassified from AOCI	0	[1],[2]	1	[1],[2]
Net current-period OCI	0	[1]	12	[1]
Ending balance	0	[1]	120	[1]
PECO Energy Co [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance					1	[1]	1	[1]
Ending balance	1	[1]	1	[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					0	[1]	0	[1]
Ending balance	0	[1]	0	[1]	0	[1]	0	[1]
PECO Energy Co [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance					1	[1]	1	[1]
Ending balance	$ 1	[1]	$ 1	[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.