Fair Value of Financial Assets and Liabilities (Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 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	$ (152)	$ 54
Change in the unrealized gains (losses) relating to assets and liabilities held	40	230
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	108	5
Change in the unrealized gains (losses) relating to assets and liabilities held	127	(16)
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
Change in the unrealized gains (losses) relating to assets and liabilities held	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	(158)	61
Change in the unrealized gains (losses) relating to assets and liabilities held	30	181
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	107	5
Change in the unrealized gains (losses) relating to assets and liabilities held	126	(16)
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
Change in the unrealized gains (losses) relating to assets and liabilities held	$ 1