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, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
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	$ (62)	$ 137	$ (330)	$ (22)
Change in the unrealized gains (losses) relating to assets and liabilities held	(10)	156	(435)	39
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	14	21	(30)	53
Change in the unrealized gains (losses) relating to assets and liabilities held	29	31	8	69
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	2	1	3	2
Change in the unrealized gains (losses) relating to assets and liabilities held	2	1	2	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	(62)	148	(330)	(28)
Change in the unrealized gains (losses) relating to assets and liabilities held	(10)	153	(435)	29
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	14	20	(30)	52
Change in the unrealized gains (losses) relating to assets and liabilities held	29	30	8	68
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	2	1	3	2
Change in the unrealized gains (losses) relating to assets and liabilities held	$ 2	$ 1	$ 2	$ 1