Basis of Presentation - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Jun. 30, 2015	Sep. 30, 2015	Sep. 30, 2014
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total interest expense to affiliates, net	$ 10	$ 11		$ 31	$ 31
Pretax decrease in operating and maintenance expense	(1,996)	(1,982)		(6,119)	(6,005)
Pretax increase in taxes other than income	310	306		908	887
Income (Loss) from Equity Method Investments		0		(3)	(20)
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions	(1)			(3)
Exelon Generation Co L L C [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Purchased power and fuel from affiliates	3	59		11	476
Total interest expense to affiliates, net	12	12		33	37
Pretax decrease in operating and maintenance expense	(1,088)	(1,114)		(3,399)	(3,308)
Pretax increase in taxes other than income	123	127		369	350
Income (Loss) from Equity Method Investments		1		(4)	(20)
Income (Loss) from Equity Method Investments, Net of Dividends or Distributions	(1)			(4)
Exelon Generation Co L L C [Member] | Scenario Adjustment [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Derivative, Gain (Loss) on Derivative, Net	52	12	$ 40
Baltimore Gas and Electric Company [Member]
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Total interest expense to affiliates, net	4	4		11	12
Purchased power and fuel	170	216		664	808
Pretax decrease in operating and maintenance expense	(138)	(142)		(412)	(468)
Pretax increase in taxes other than income	$ 57	$ 55		$ 169	168
Income (Loss) from Equity Method Investments					$ 0