Basis of Presentation - Narrative (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2014	Mar. 31, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Total interest expense to affiliates, net	$ 11		$ 6	$ 31	$ 19
Pretax decrease in operating and maintenance expense	(1,982)	(1)	(1,735)	(6,005)	(5,391)
Pretax increase in taxes other than income	306		277	887	825
Scenario Adjustment [Member]
Purchased power and fuel from affiliates			339		944
Exelon Generation Co L L C [Member]
Purchased power and fuel from affiliates	59		342	476	953
Total interest expense to affiliates, net	12		13	37	47
Pretax decrease in operating and maintenance expense	(1,114)		(936)	(3,308)	(2,943)
Pretax increase in taxes other than income	127		98	350	292
Exelon Generation Co L L C [Member] | Scenario Adjustment [Member]
Purchased power and fuel from affiliates			342		953
Total interest expense to affiliates, net			13		47
Baltimore Gas and Electric Company [Member]
Total interest expense to affiliates, net	4		4	12	12
Purchased power and fuel	216		202	808	703
Pretax decrease in operating and maintenance expense	(142)		(125)	(468)	(391)
Pretax increase in taxes other than income	55		53	168	162
Baltimore Gas and Electric Company [Member] | Scenario Adjustment [Member]
Total interest expense to affiliates, net			$ 4		$ 12