Changes in Accumulated Other Comprehensive Income (Changes in accumulated other comprehensive income by component)(Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012	Mar. 31, 2013 Accumulated Net Gain Loss From Designated Or Qualifying Cash Flow Hedges [Member]		Mar. 31, 2013 Accumulated Net Unrealized Investment Gain Loss [Member]		Mar. 31, 2013 Accumulated Defined Benefit Plans Adjustment [Member]		Mar. 31, 2013 Accumulated Translation Adjustment [Member]		Mar. 31, 2013 Accumulated Equity Investment [Member]		Mar. 31, 2013 Exelon Generation Co L L C [Member]		Mar. 31, 2012 Exelon Generation Co L L C [Member]	Mar. 31, 2013 Exelon Generation Co L L C [Member] Accumulated Net Gain Loss From Designated Or Qualifying Cash Flow Hedges [Member]		Mar. 31, 2013 Exelon Generation Co L L C [Member] Accumulated Net Unrealized Investment Gain Loss [Member]		Mar. 31, 2013 Exelon Generation Co L L C [Member] Accumulated Defined Benefit Plans Adjustment [Member]		Mar. 31, 2013 Exelon Generation Co L L C [Member] Accumulated Translation Adjustment [Member]		Mar. 31, 2013 Exelon Generation Co L L C [Member] Accumulated Equity Investment [Member]		Mar. 31, 2013 Commonwealth Edison Co [Member]	Mar. 31, 2012 Commonwealth Edison Co [Member]	Mar. 31, 2013 PECO Energy Co [Member]		Mar. 31, 2012 PECO Energy Co [Member]	Mar. 31, 2013 PECO Energy Co [Member] Accumulated Net Unrealized Investment Gain Loss [Member]		Dec. 31, 2012 PECO Energy Co [Member] Accumulated Net Unrealized Investment Gain Loss [Member]		Mar. 31, 2013 Baltimore Gas and Electric Company [Member] Accumulated Net Gain Loss From Designated Or Qualifying Cash Flow Hedges [Member]		Dec. 31, 2012 Baltimore Gas and Electric Company [Member] Accumulated Net Gain Loss From Designated Or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax, Beginning Balance	$ (2,767)	[1]		$ 368	[1]	$ 0	[1]	$ (3,137)	[1]	$ 0	[1]	$ 2	[1]	$ 513	[1]		$ 513	[1]	$ (1)	[1]	$ (19)	[1]			$ 20	[1]	$ 0		$ 1	[1]		$ 1	[1]	$ 1	[1]	$ 0	[1]	$ 0	[1]
OCI before reclassifications	100	[1]		0	[1]	(1)	[1]	76	[1]	(1)	[1]	26	[1]	29	[1]		5	[1]	(1)	[1]	0	[1]	(1)	[1]	26	[1]
Amounts reclassified from AOCI	(6)	[1],[2]		(58)	[1],[2]			50	[1],[2]			2	[1],[2]	(133)	[1],[2]		(135)	[1],[2]							2	[1],[2]
Net current-period OCI	94	[1]	251	(58)	[1]	(1)	[1]	126	[1]	(1)	[1]	28	[1]	(104)	[1]	252	(130)	[1]	(1)	[1]	0	[1]	(1)	[1]	28	[1]	0	1	0		1
Accumulated Other Comprehensive Income (Loss), Net of Tax, Ending Balance	$ (2,673)	[1]		$ 310	[1]	$ (1)	[1]	$ (3,011)	[1]	$ (1)	[1]	$ 30	[1]	$ 409	[1]		$ 383	[1]	$ (2)	[1]	$ (19)	[1]	$ (1)	[1]	$ 48	[1]	$ 0		$ 1	[1]		$ 1	[1]	$ 1	[1]	$ 0	[1]	$ 0	[1]

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

[2] (b) See next table for details about these reclassifications.