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			6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012	Jun. 30, 2013		Jun. 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	$ 137		$ (69)	$ (22)		$ 23
Change in the unrealized gains (losses) relating to assets and liabilities held	156		5	39		125
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	21		5	53		(4)
Change in the unrealized gains (losses) relating to assets and liabilities held	31		(3)	69		(21)
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	1	[1]		2	[1]
Change in the unrealized gains (losses) relating to assets and liabilities held	1	[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	148		(74)	(28)		7
Change in the unrealized gains (losses) relating to assets and liabilities held	153		(10)	29		99
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	20		5	52		(4)
Change in the unrealized gains (losses) relating to assets and liabilities held	30		(3)	68		(21)
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	1	[2]		2	[2]
Change in the unrealized gains (losses) relating to assets and liabilities held	$ 1	[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.