Changes in Accumulated Other Comprehensive Income - Components of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	[1]	$ (2,626)	$ (1,906)	$ (2,626)	$ (1,906)	$ (2,684)	$ (2,040)
Pension and non-pension postretirement benefit plans:
Prior service benefit reclassified to periodic benefit cost		8	5	15	5
Actuarial loss reclassified to periodic cost		(35)	(23)	(69)	(46)
Pension and non-pension postretirement benefit plans valuation adjustment		0	(166)	17	(159)
Change in unrealized (gain) loss on cash flow hedges		(2)	28	(6)	48
Change in unrealized income on equity investments		0	77	0	70
Change in marketable securities		1		1	0
Total		(28)	(79)	(42)	(82)
Exelon Generation Co L L C [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	[1]	(47)	37	(47)	37	$ (36)	$ 214
Pension and non-pension postretirement benefit plans:
Change in unrealized (gain) loss on cash flow hedges		(1)	25	1	44
Change in unrealized income on equity investments		0	77	0	70
Change in marketable securities		0	0	1	(2)
Total		$ (1)	$ 102	$ 2	$ 112

[1] All amounts are net of tax. Amounts in parentheses represent a decrease in accumulated other comprehensive income.