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, 2016		Dec. 31, 2015	Dec. 31, 2014
Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	[1]	$ 284		$ 284		$ 311	$ 272
Charged to Costs and Expenses	[1]			162		113	175
Charged to Other Accounts	[1],[2]			99	[3]	27	69
Deductions	[1],[4]			211		167	205
Balance at End of Period	[1]		$ 334	334		284	311
Deferred Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		13		13		50	13
Charged to Costs and Expenses				0		0	0
Charged to Other Accounts				10	[3]	(27)	37
Deductions				3		10	0
Balance at End of Period			20	20		13	50
Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		105		105		95	58
Charged to Costs and Expenses				12		10	5
Charged to Other Accounts				1	[3]	2	34
Deductions				5		2	2
Balance at End of Period			113	113		105	95
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		77		60	57
Charged to Costs and Expenses				19		22	14
Charged to Other Accounts				3		0	8
Deductions				8		5	19
Balance at End of Period			91	91		77	60
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		11		48	11
Charged to Costs and Expenses				0		0	0
Charged to Other Accounts				0		(27)	37
Deductions				2		10	0
Balance at End of Period			9	9		11	48
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		102		93	55
Charged to Costs and Expenses				6		9	5
Charged to Other Accounts				0		0	32
Deductions				2		0	(1)
Balance at End of Period			106	106		102	93
Commonwealth Edison Co [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		75		75		84	62
Charged to Costs and Expenses				45		39	45
Charged to Other Accounts	[5]			23		18	33
Deductions	[6]			73		66	56
Balance at End of Period			70	70		75	84
Commonwealth Edison Co [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		3		3		2	2
Charged to Costs and Expenses				4		1	0
Charged to Other Accounts				1		2	2
Deductions				4		2	2
Balance at End of Period			4	4		3	2
PECO Energy Co [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	[7]	83		83		100	107
Charged to Costs and Expenses	[7]			32		37	52
Charged to Other Accounts	[7],[8]			7		9	11
Deductions	[7],[9]			61		63	70
Balance at End of Period	[7]		61	61		83	100
PECO Energy Co [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		1		1		1	1
Charged to Costs and Expenses				1		0	0
Charged to Other Accounts				0		0	0
Deductions				0		0	0
Balance at End of Period			2	2		1	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		8		8
Balance at End of Period			23	23		8	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		49		67	46
Charged to Costs and Expenses				1		15	64
Charged to Other Accounts	[10]			9		0	17
Deductions	[11]			27		33	60
Balance at End of Period			32	32		49	67
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	1
Charged to Costs and Expenses				0		0	0
Charged to Other Accounts				0		0	0
Deductions				0		0	1
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
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		17		16	16
Charged to Costs and Expenses				29		20	17
Charged to Other Accounts	[12]			3		1	2
Deductions	[13]			20		20	19
Balance at End of Period			29	29		17	16
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		0		0	0
Charged to Costs and Expenses				3		0	0
Charged to Other Accounts				0		0	0
Deductions				2		0	0
Balance at End of Period			1	1		0	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		17		11	12
Charged to Costs and Expenses				23		20	13
Charged to Other Accounts	[14]			2		2	4
Deductions	[15]			18		16	18
Balance at End of Period			24	24		17	11
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		0	0
Charged to Other Accounts				0		0	0
Deductions				1		0	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		17		9	10
Charged to Costs and Expenses				32		18	12
Charged to Other Accounts	[16]			2		2	3
Deductions	[17]			24		12	16
Balance at End of Period			27	27		17	9
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		0		0	0
Charged to Costs and Expenses				1		0	0
Charged to Other Accounts				0		0	0
Deductions				0		0	0
Balance at End of Period			1	1		0	0
Successor [Member] | Pepco Holdings LLC [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period			52
Charged to Costs and Expenses			65
Charged to Other Accounts	[18]		5
Deductions	[19]		42
Balance at End of Period		52	80	80
Successor [Member] | Pepco Holdings LLC [Member] | Deferred Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period			63
Charged to Costs and Expenses			0
Charged to Other Accounts			(53)
Deductions			0
Balance at End of Period		63	10	10
Successor [Member] | Pepco Holdings LLC [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period			0
Charged to Costs and Expenses			1
Charged to Other Accounts			0
Deductions			(1)
Balance at End of Period		0	2	2
Predecessor [Member] | Pepco Holdings LLC [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		56	52	56		40	38
Charged to Costs and Expenses		16				59	46
Charged to Other Accounts	[18]	2				5	9
Deductions	[19]	22				48	53
Balance at End of Period		52				56	40
Predecessor [Member] | Pepco Holdings LLC [Member] | Deferred Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		63	63	63		61	21
Charged to Costs and Expenses		0				0	0
Charged to Other Accounts		0				2	40
Deductions		0				0	0
Balance at End of Period		63				63	61
Predecessor [Member] | Pepco Holdings LLC [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0	$ 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

[1] Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $23 million, $8 million, and $8 million for the years ended December 31, 2016, 2015, and 2014, 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 $23 million, $8 million, and $8 million for the years ended December 31, 2016, 2015, and 2014, respectively.

[8] Primarily charges for late payments.

[9] Write-off of individual accounts receivable.

[10] Primarily charges for late payments.

[11] Write-off of individual accounts receivable.

[12] Primarily charges for late payments.

[13] Write-off of individual accounts receivable.

[14] Primarily charges for late payments.

[15] Write-off of individual accounts receivable.

[16] Primarily charges for late payments.

[17] Write-off of individual accounts receivable.

[18] Primarily charges for late payments.

[19] Write-off of individual accounts receivable.