Changes in Accumulated Other Comprehensive Income (Changes in accumulated other comprehensive income by component)(Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended											3 Months Ended			6 Months Ended														6 Months Ended
	Jun. 30, 2012	Jun. 30, 2013		Jun. 30, 2012	Jun. 30, 2013 Accumulated Net Gain Loss From Designated Or Qualifying Cash Flow Hedges [Member]		Jun. 30, 2013 Accumulated Defined Benefit Plans Adjustment [Member]		Jun. 30, 2013 Accumulated Translation Adjustment [Member]		Jun. 30, 2013 Accumulated Equity Investment [Member]		Jun. 30, 2013 Exelon Generation Co L L C [Member]		Jun. 30, 2012 Exelon Generation Co L L C [Member]	Jun. 30, 2013 Exelon Generation Co L L C [Member]		Jun. 30, 2012 Exelon Generation Co L L C [Member]	Jun. 30, 2013 Exelon Generation Co L L C [Member] Accumulated Net Gain Loss From Designated Or Qualifying Cash Flow Hedges [Member]		Jun. 30, 2013 Exelon Generation Co L L C [Member] Accumulated Net Unrealized Investment Gain Loss [Member]		Jun. 30, 2013 Exelon Generation Co L L C [Member] Accumulated Translation Adjustment [Member]		Jun. 30, 2013 Exelon Generation Co L L C [Member] Accumulated Equity Investment [Member]		Jun. 30, 2012 Commonwealth Edison Co [Member]	Jun. 30, 2013 Commonwealth Edison Co [Member]	Dec. 31, 2012 Commonwealth Edison Co [Member]	Jun. 30, 2012 PECO Energy Co [Member]	Jun. 30, 2013 PECO Energy Co [Member]		Dec. 31, 2012 PECO Energy Co [Member]		Jun. 30, 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]		Jun. 30, 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]	$ (3,137)	[1]	$ 0	[1]	$ 2	[1]				$ 513	[1]		$ 512	[1]					$ 1	[1]		$ 0	$ 0		$ 1	[1]	$ 1	[1]	$ 1	[1]	$ 1	[1]	$ 0	[1]	$ 0	[1]
OCI before reclassifications		135	[1]		24	[1]	87	[1]	(6)	[1]	31	[1]				36	[1]		12	[1]	(1)	[1]	(6)	[1]	31	[1]
Amounts reclassified from AOCI		(41)	[1],[2]		(147)	[1],[2]	101	[1],[2]			5	[1],[2]				(274)	[1],[2]		(279)	[1],[2]					5	[1],[2]
Net current-period OCI	(114)	94	[1]	137	(123)	[1]	188	[1]	(6)	[1]	36	[1]	(134)		(263)	(238)	[1]	(11)	(267)	[1]	(1)	[1]	(6)	[1]	36	[1]	1			1
Accumulated Other Comprehensive Income (Loss), Net of Tax, Ending Balance		$ (2,673)	[1]		$ 245	[1]	$ (2,949)	[1]	$ (6)	[1]	$ 38	[1]	$ 275	[1]		$ 275	[1]		$ 245	[1]	$ (1)	[1]	$ (6)	[1]	$ 37	[1]		$ 0	$ 0		$ 1	[1]	$ 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.