Fair Value of Financial Assets and Liabilities (Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings) (Details) (Fair Value Inputs Level 3 [Member], USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012
Operating Revenue [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Total gains (losses) included in income	$ (39)		$ (101)	$ (61)		$ (78)
Change in the unrealized gains (losses) relating to assets and liabilities held	42		(43)	81		82
Purchased Fuel and Electric [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Total gains (losses) included in income	7		4	60		0
Change in the unrealized gains (losses) relating to assets and liabilities held	9		1	78		(20)
Other, net [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Total gains (losses) included in income	0	[1]		2	[1]
Change in the unrealized gains (losses) relating to assets and liabilities held	0	[1]		1	[1]
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Total gains (losses) included in income	(39)		(116)	(67)		(109)
Change in the unrealized gains (losses) relating to assets and liabilities held	42		(78)	71		21
Exelon Generation Co L L C [Member] | Purchased Fuel and Electric [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Total gains (losses) included in income	7		4	59		0
Change in the unrealized gains (losses) relating to assets and liabilities held	9		1	77		(20)
Exelon Generation Co L L C [Member] | Other, net [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Total gains (losses) included in income	0	[2]		2	[2]
Change in the unrealized gains (losses) relating to assets and liabilities held	$ 0	[2]		$ 1	[2]

[1] Other, net activity consists of realized and unrealized gains (losses) included in income for the NDT funds held by Generation.

[2]         Other, net activity consists of realized and unrealized gains (losses) included in income for the NDT funds held by Generation.