Basis of Presentation - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total interest expense to affiliates, net	$ 10	$ 10	$ 21	$ 20
Pretax decrease in operating and maintenance expense	(2,042)	(2,166)	(4,123)	(4,024)
Pretax increase in taxes other than income	294	288	598	580
Income (Loss) from Equity Method Investments	0	0	(2)	(20)
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions	(2)	0	(2)	0
Exelon Generation Co L L C [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Purchased power and fuel from affiliates	1	69	8	417
Total interest expense to affiliates, net	9	12	21	25
Pretax decrease in operating and maintenance expense	(1,149)	(1,255)	(2,311)	(2,194)
Pretax increase in taxes other than income	124	118	246	223
Income (Loss) from Equity Method Investments		(1)	(3)	(20)
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions	(2)		(3)
Baltimore Gas and Electric Company [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total interest expense to affiliates, net	4	4	8	8
Purchased power and fuel	143	183	493	592
Pretax decrease in operating and maintenance expense	(120)	(163)	(276)	(326)
Pretax increase in taxes other than income	$ 54	$ 53	$ 111	113
Income (Loss) from Equity Method Investments				$ 0