Supplemental Financial Information - Balance Sheet (Details) - USD ($) $ in Millions		Mar. 31, 2019		Dec. 31, 2018		Mar. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation and amortization		$ 23,695	[1]	$ 22,902	[2]
Accounts receivable, net
Allowance for uncollectible accounts		340		319
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		880		1,349		$ 787	$ 898
Restricted cash and cash equivalents		223		247		209	207
Restricted cash included in other long-term assets		211		185		103	85
Total cash, cash equivalents and restricted cash		1,314		1,781		1,099	1,190
Purchased Receivables [Abstract]
Purchased receivables		332		313
Allowance for uncollectible accounts	[3]	(38)		(34)
Purchased receivables, net		294		279
Nuclear Fuel [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation and amortization		3,040		2,969
Exelon Generation Co L L C [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation and amortization		12,663	[1]	12,206	[2]
Accounts receivable, net
Allowance for uncollectible accounts		87		104
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		537		750		610	416
Restricted cash and cash equivalents		139		153		127	138
Restricted cash included in other long-term assets		0		0		0	0
Total cash, cash equivalents and restricted cash		676		903		737	554
Exelon Generation Co L L C [Member] | Nuclear Fuel [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation and amortization		3,040		2,969
Commonwealth Edison Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation and amortization		4,833		4,684
Accounts receivable, net
Allowance for uncollectible accounts		97		81
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		68		135		70	76
Restricted cash and cash equivalents		17		29		9	5
Restricted cash included in other long-term assets		193		166		83	63
Total cash, cash equivalents and restricted cash		278		330		162	144
Purchased Receivables [Abstract]
Purchased receivables		105		94
Allowance for uncollectible accounts	[3]	(19)		(17)
Purchased receivables, net		86		77
PECO Energy Co [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation and amortization		3,598		3,561
Accounts receivable, net
Allowance for uncollectible accounts		72		61
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		41		130		21	271
Restricted cash and cash equivalents		6		5		5	4
Restricted cash included in other long-term assets		0		0		0	0
Total cash, cash equivalents and restricted cash		47		135		26	275
Purchased Receivables [Abstract]
Purchased receivables		77		74
Allowance for uncollectible accounts	[3]	(6)		(5)
Purchased receivables, net		71		69
Baltimore Gas and Electric Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation and amortization		3,670		3,633
Accounts receivable, net
Allowance for uncollectible accounts		27		20
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		12		7		22	17
Restricted cash and cash equivalents		4		6		2	1
Restricted cash included in other long-term assets		0		0		0	0
Total cash, cash equivalents and restricted cash		16		13		24	18
Purchased Receivables [Abstract]
Purchased receivables		65		61
Allowance for uncollectible accounts	[3]	(4)		(3)
Purchased receivables, net		61		58
Pepco Holdings LLC [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation and amortization		930		841
Accounts receivable, net
Allowance for uncollectible accounts		57		53
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		33		124		43	30
Restricted cash and cash equivalents		39		43		40	42
Restricted cash included in other long-term assets		19		19		20	23
Total cash, cash equivalents and restricted cash		91		186		103	95
Purchased Receivables [Abstract]
Purchased receivables		85		84
Allowance for uncollectible accounts	[3]	(9)		(9)
Purchased receivables, net		76		75
Potomac Electric Power Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation and amortization		3,392		3,354
Accounts receivable, net
Allowance for uncollectible accounts		23		21
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		11		16		15	5
Restricted cash and cash equivalents		35		37		33	35
Restricted cash included in other long-term assets		0		0		0	0
Total cash, cash equivalents and restricted cash		46		53		48	40
Purchased Receivables [Abstract]
Purchased receivables		58		57
Allowance for uncollectible accounts	[3]	(5)		(5)
Purchased receivables, net		53		52
Delmarva Power and Light Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation and amortization		1,354		1,329
Accounts receivable, net
Allowance for uncollectible accounts		15		13
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		7		23		7	2
Restricted cash and cash equivalents		1		1		0	0
Restricted cash included in other long-term assets		0		0		0	0
Total cash, cash equivalents and restricted cash		8		24		7	2
Purchased Receivables [Abstract]
Purchased receivables		8		8
Allowance for uncollectible accounts	[3]	(1)		(1)
Purchased receivables, net		7		7
Atlantic City Electric Company [Member]
Property, Plant and Equipment, Net [Abstract]
Accumulated depreciation and amortization		1,154		1,137
Accounts receivable, net
Allowance for uncollectible accounts		19		19
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents		6		7		10	2
Restricted cash and cash equivalents		3		4		7	6
Restricted cash included in other long-term assets		19		19		20	23
Total cash, cash equivalents and restricted cash		28		30		$ 37	$ 31
Purchased Receivables [Abstract]
Purchased receivables		19		19
Allowance for uncollectible accounts	[3]	(3)		(3)
Purchased receivables, net		$ 16		$ 16

[1] Includes accumulated amortization of nuclear fuel in the reactor core of $3,040 million.

[2] Includes accumulated amortization of nuclear fuel in the reactor core of $2,969 million.

[3] For ComEd, BGE, Pepco and DPL, reflects the incremental allowance for uncollectible accounts recorded, which is in addition to the purchase discount. For ComEd, the incremental uncollectible accounts expense is recovered through a rate rider. BGE, Pepco and DPL recover actual write-offs which are reflected in the POR discount rate.