Changes in Accumulated Other Comprehensive Income - Components of Other Comprehensive Income (Loss) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Pension and non-pension postretirement benefit plans:
Prior service benefit reclassified to periodic benefit cost	$ 8	$ 0	$ 11	$ 0
Actuarial gain (loss) reclassified to periodic cost	(24)	33	(69)	97
Pension and non-pension postretirement benefit plans valuation adjustment	5	(6)	(153)	44
Change in unrealized gain (loss) on cash flow hedges	15	(35)	62	(109)
Change in unrealized income on equity investments	3	9	73	32
Deferred compensation unit valuation adjustment	0	0	0	6
Change in marketable securities	1	0	(1)	0
Total	8	1	(77)	70
Exelon Generation Co L L C [Member]
Pension and non-pension postretirement benefit plans:
Change in unrealized gain (loss) on cash flow hedges	13	(36)	57	(209)
Change in unrealized income on equity investments	3	9	73	32
Change in marketable securities	1	0	(1)	0
Total	$ 17	$ (27)	$ 129	$ (177)