Schedule II - Valuation and Qualifying Accounts Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015
Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	[1]	$ 284		$ 334	$ 284		$ 311
Charged to Costs and Expenses	[1]			126	162		113
Charged to Other Accounts	[1],[2]			27	99	[3]	27
Deductions	[1],[4]			165	211		167
Balance at End of Period	[1]		$ 334	322	334		284
Deferred Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		13		20	13		50
Charged to Costs and Expenses				0	0		0
Charged to Other Accounts				17	10	[3]	(27)
Deductions				0	3		10
Balance at End of Period			20	37	20		13
Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		105		113	105		95
Charged to Costs and Expenses				56	12		10
Charged to Other Accounts				10	1	[3]	2
Deductions				5	5		2
Balance at End of Period			113	174	113		105
Exelon Generation Co L L C [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		77		91	77		60
Charged to Costs and Expenses				34	19		22
Charged to Other Accounts				0	3		0
Deductions				11	8		5
Balance at End of Period			91	114	91		77
Exelon Generation Co L L C [Member] | Deferred Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		11		9	11		48
Charged to Costs and Expenses				0	0		0
Charged to Other Accounts				14	0		(27)
Deductions				0	2		10
Balance at End of Period			9	23	9		11
Exelon Generation Co L L C [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		102		106	102		93
Charged to Costs and Expenses				51	6		9
Charged to Other Accounts				9	0		0
Deductions				0	2		0
Balance at End of Period			106	166	106		102
Commonwealth Edison Co [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		75		70	75		84
Charged to Costs and Expenses				39	45		39
Charged to Other Accounts	[5]			20	23		18
Deductions	[6]			56	73		66
Balance at End of Period			70	73	70		75
Commonwealth Edison Co [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		3		4	3		2
Charged to Costs and Expenses				3	4		1
Charged to Other Accounts				1	1		2
Deductions				3	4		2
Balance at End of Period			4	5	4		3
PECO Energy Co [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	[7]	83		61	83		100
Charged to Costs and Expenses	[7]			26	32		37
Charged to Other Accounts	[7],[8]			4	7		9
Deductions	[7],[9]			35	61		63
Balance at End of Period	[7]		61	56	61		83
PECO Energy Co [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		1		2	1		1
Charged to Costs and Expenses				0	1		0
Charged to Other Accounts				0	0		0
Deductions				0	0		0
Balance at End of Period			2	2	2		1
PECO Energy Co [Member] | Allowance for Doubtful Accounts, Noncurrent [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		8		23	8
Balance at End of Period			23	15	23		8
Baltimore Gas and Electric Company [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		49		32	49		67
Charged to Costs and Expenses				8	1		15
Charged to Other Accounts				(3)	9		0
Deductions	[10]			13	27		33
Balance at End of Period			32	24	32		49
Baltimore Gas and Electric Company [Member] | Deferred Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		1		1	1		1
Charged to Costs and Expenses				0	0		0
Charged to Other Accounts				0	0		0
Deductions				0	0		0
Balance at End of Period			1	1	1		1
Baltimore Gas and Electric Company [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0		0	0		0
Charged to Costs and Expenses				0	0		0
Charged to Other Accounts				0	0		0
Deductions				0	0		0
Balance at End of Period			0	0	0		0
Pepco Holdings LLC [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Charged to Costs and Expenses				10
Pepco Holdings LLC [Member] | Allowance for Uncollectible Accounts [Member] | Successor [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period			52	80
Charged to Costs and Expenses			65	19
Charged to Other Accounts	[11]		5	6
Deductions	[12]		42	50
Balance at End of Period		52	80	55	80
Pepco Holdings LLC [Member] | Allowance for Uncollectible Accounts [Member] | Predecessor [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		56	52		56		40
Charged to Costs and Expenses		16					59
Charged to Other Accounts	[11]	2					5
Deductions	[12]	22					48
Balance at End of Period		52					56
Pepco Holdings LLC [Member] | Deferred Tax Valuation Allowance [Member] | Successor [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period			63	10
Charged to Costs and Expenses			0	0
Charged to Other Accounts			(53)	3
Deductions			0	0
Balance at End of Period		63	10	13	10
Pepco Holdings LLC [Member] | Deferred Tax Valuation Allowance [Member] | Predecessor [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		63	63		63		61
Charged to Costs and Expenses		0					0
Charged to Other Accounts		0					2
Deductions		0					0
Balance at End of Period		63					63
Pepco Holdings LLC [Member] | Reserve for Obsolete Materials [Member] | Successor [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period			0	2
Charged to Costs and Expenses			1	2
Charged to Other Accounts			0	0
Deductions			(1)	2
Balance at End of Period		0	2	2	2
Pepco Holdings LLC [Member] | Reserve for Obsolete Materials [Member] | Predecessor [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0	0		0		0
Charged to Costs and Expenses		0					0
Charged to Other Accounts		0					0
Deductions		0					0
Balance at End of Period		0					0
Potomac Electric Power Company [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Charged to Costs and Expenses				6
Potomac Electric Power Company [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		17		29	17		16
Charged to Costs and Expenses				8	29		20
Charged to Other Accounts	[13]			2	3		1
Deductions	[14]			18	20		20
Balance at End of Period			29	21	29		17
Potomac Electric Power Company [Member] | Deferred Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0		0	0		0
Charged to Costs and Expenses				0	0		0
Charged to Other Accounts				0	0		0
Deductions				0	0		0
Balance at End of Period			0	0	0		0
Potomac Electric Power Company [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0		1	0		0
Charged to Costs and Expenses				1	3		0
Charged to Other Accounts				0	0		0
Deductions				1	2		0
Balance at End of Period			1	1	1		0
Delmarva Power and Light Company [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Charged to Costs and Expenses				4
Delmarva Power and Light Company [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		17		24	17		11
Charged to Costs and Expenses				3	23		20
Charged to Other Accounts	[15]			2	2		2
Deductions	[16]			13	18		16
Balance at End of Period			24	16	24		17
Delmarva Power and Light Company [Member] | Deferred Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0		0	0		0
Charged to Costs and Expenses				0	0		0
Charged to Other Accounts				0	0		0
Deductions				0	0		0
Balance at End of Period			0	0	0		0
Delmarva Power and Light Company [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0		0	0		0
Charged to Costs and Expenses				1	1		0
Charged to Other Accounts				0	0		0
Deductions				1	1		0
Balance at End of Period			0	0	0		0
Atlantic City Electric Company [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		17		27	17		9
Charged to Costs and Expenses				8	32		18
Charged to Other Accounts	[17]			2	2		2
Deductions	[18]			19	24		12
Balance at End of Period			27	18	27		17
Atlantic City Electric Company [Member] | Deferred Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0		0	0		0
Charged to Costs and Expenses				0	0		0
Charged to Other Accounts				0	0		0
Deductions				0	0		0
Balance at End of Period			0	0	0		0
Atlantic City Electric Company [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		$ 0		1	0		0
Charged to Costs and Expenses				0	1		0
Charged to Other Accounts				0	0		0
Deductions				0	0		0
Balance at End of Period			$ 1	$ 1	$ 1		$ 0

[1] Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $15 million, $23 million, and $8 million for the years ended December 31, 2017, 2016, and 2015, respectively.

[2] Includes charges for late payments and non-service receivables.

[3] Primarily represents the addition of PHI's results as of March 23, 2016, the date of the merger

[4] Write-off of individual accounts receivable.

[5] Primarily charges for late payments and non-service receivables.

[6] Write-off of individual accounts receivable.

[7] Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $15 million, $23 million, and $8 million for the years ended December 31, 2017, 2016, and 2015, respectively.

[8] Primarily charges for late payments.

[9] Write-off of individual accounts receivable.

[10] Write-off of individual accounts receivable.

[11] Primarily charges for late payments.

[12] Write-off of individual accounts receivable.

[13] Primarily charges for late payments.

[14] Write-off of individual accounts receivable.

[15] Primarily charges for late payments.

[16] Write-off of individual accounts receivable.

[17] Primarily charges for late payments.

[18] Write-off of individual accounts receivable.