Supplemental Financial Information - Balance Sheet (Details) - USD ($) $ in Millions	Jun. 30, 2018		Dec. 31, 2017		Jun. 30, 2017	Dec. 31, 2016
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	$ 22,302	[1]	$ 21,064	[2]
Accounts receivable, net
Allowance for uncollectible accounts	339		322
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and Cash Equivalents, at Carrying Value	694		898		$ 536	$ 635
Restricted cash	206		207		252	253
Restricted Cash, Noncurrent	128		85		23	26
Cash, Cash Equivalents and Restricted Cash at End of Period	1,028		1,190		811	914
Exelon Generation Co L L C [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	12,143	[1]	11,428	[2]
Accounts receivable, net
Allowance for uncollectible accounts	123		114
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and Cash Equivalents, at Carrying Value	420		416		265	290
Restricted cash	130		138		166	158
Restricted Cash, Noncurrent	0		0		0	0
Cash, Cash Equivalents and Restricted Cash at End of Period	550		554		431	448
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,094		3,159
Commonwealth Edison Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	4,491		4,269
Accounts receivable, net
Allowance for uncollectible accounts	82		73
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and Cash Equivalents, at Carrying Value	30		76		39	56
Restricted cash	5		5		12	2
Restricted Cash, Noncurrent	108		63		0	0
Cash, Cash Equivalents and Restricted Cash at End of Period	143		144		51	58
PECO Energy Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,482		3,411
Accounts receivable, net
Allowance for uncollectible accounts	57		56
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and Cash Equivalents, at Carrying Value	18		271		45	63
Restricted cash	5		4		4	4
Restricted Cash, Noncurrent	0		0		0	0
Cash, Cash Equivalents and Restricted Cash at End of Period	23		275		49	67
Baltimore Gas and Electric Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,530		3,405
Accounts receivable, net
Allowance for uncollectible accounts	21		24
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and Cash Equivalents, at Carrying Value	7		17		12	23
Restricted cash	1		1		6	24
Restricted Cash, Noncurrent	0		0		0	3
Cash, Cash Equivalents and Restricted Cash at End of Period	8		18		18	50
Pepco Holdings LLC [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	671		487
Accounts receivable, net
Allowance for uncollectible accounts	55		55
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and Cash Equivalents, at Carrying Value	195		30		151	170
Restricted cash	38		42		40	43
Restricted Cash, Noncurrent	20		23		23	23
Cash, Cash Equivalents and Restricted Cash at End of Period	253		95		214	236
Potomac Electric Power Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	3,269		3,177
Accounts receivable, net
Allowance for uncollectible accounts	23		21
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and Cash Equivalents, at Carrying Value	47		5		119	9
Restricted cash	33		35		34	33
Restricted Cash, Noncurrent	0		0		0	0
Cash, Cash Equivalents and Restricted Cash at End of Period	80		40		153	42
Delmarva Power and Light Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	1,295		1,247
Accounts receivable, net
Allowance for uncollectible accounts	14		16
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and Cash Equivalents, at Carrying Value	141		2		6	46
Restricted cash	0		0		0	0
Restricted Cash, Noncurrent	0		0		0	0
Cash, Cash Equivalents and Restricted Cash at End of Period	141		2		6	46
Atlantic City Electric Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation	1,105		1,066
Accounts receivable, net
Allowance for uncollectible accounts	18		18
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and Cash Equivalents, at Carrying Value	6		2		7	101
Restricted cash	5		6		7	9
Restricted Cash, Noncurrent	20		23		23	23
Cash, Cash Equivalents and Restricted Cash at End of Period	$ 31		$ 31		$ 37	$ 133

[1] Includes accumulated amortization of nuclear fuel in the reactor core of $3,094 million.

[2] Includes accumulated amortization of nuclear fuel in the reactor core of $3,159 million.