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, 2018		Dec. 31, 2017	Dec. 31, 2016
Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	[1]	$ 284		$ 322		$ 334	$ 284
Charged to Costs and Expenses	[1]			159		126	162
Charged to Other Accounts	[1],[2]			35		27	99	[3]
Deductions	[1],[4]			197		165	211
Balance at End of Period	[1]		$ 334	319		322	334
Deferred Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		13		37		20	13
Charged to Costs and Expenses				0		0	0
Charged to Other Accounts				5		17	10	[3]
Deductions				7		0	3
Balance at End of Period			20	35		37	20
Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		105		174		113	105
Charged to Costs and Expenses				25		56	12
Charged to Other Accounts				(31)	[5]	10	1	[3]
Deductions				12		5	5
Balance at End of Period			113	156		174	113
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		114		91	77
Charged to Costs and Expenses				44		34	19
Charged to Other Accounts				4		0	3
Deductions				58		11	8
Balance at End of Period			91	104		114	91
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		23		9	11
Charged to Costs and Expenses				0		0	0
Charged to Other Accounts				3		14	0
Deductions				0		0	2
Balance at End of Period			9	26		23	9
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		166		106	102
Charged to Costs and Expenses				20		51	6
Charged to Other Accounts				(32)	[6]	9	0
Deductions				9		0	2
Balance at End of Period			106	145		166	106
Commonwealth Edison Co [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		75		73		70	75
Charged to Costs and Expenses				44		39	45
Charged to Other Accounts	[7]			23		20	23
Deductions	[8]			59		56	73
Balance at End of Period			70	81		73	70
Commonwealth Edison Co [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		3		5		4	3
Charged to Costs and Expenses				3		3	4
Charged to Other Accounts				1		1	1
Deductions				3		3	4
Balance at End of Period			4	6		5	4
PECO Energy Co [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	[9]	83		56		61	83
Charged to Costs and Expenses	[9]			33		26	32
Charged to Other Accounts	[9],[10]			3		4	7
Deductions	[9],[11]			31		35	61
Balance at End of Period	[9]		61	61		56	61
PECO Energy Co [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		1		2		2	1
Charged to Costs and Expenses				0		0	1
Charged to Other Accounts				0		0	0
Deductions				0		0	0
Balance at End of Period			2	2		2	2
PECO Energy Co [Member] | Allowance for Doubtful Accounts, Noncurrent [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period				15		23
Balance at End of Period			23	13		15	23
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		24		32	49
Charged to Costs and Expenses				10		8	1
Charged to Other Accounts				(2)		(3)	9
Deductions	[12]			12		13	27
Balance at End of Period			32	20		24	32
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				1		0	0
Charged to Other Accounts				0		0	0
Deductions				0		0	0
Balance at End of Period			0	1		0	0
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	55		80
Charged to Costs and Expenses			65	28		19
Charged to Other Accounts	[13]		5	7		6
Deductions	[14]		42	37		50
Balance at End of Period		52	80	53		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
Charged to Costs and Expenses		16
Charged to Other Accounts	[13]	2
Deductions	[14]	22
Balance at End of Period		52
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	13		10
Charged to Costs and Expenses			0	0		0
Charged to Other Accounts			(53)	2		3
Deductions			0	7		0
Balance at End of Period		63	10	8		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
Charged to Costs and Expenses		0
Charged to Other Accounts		0
Deductions		0
Balance at End of Period		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		2
Charged to Costs and Expenses			1	0		2
Charged to Other Accounts			0	0		0
Deductions			(1)	0		2
Balance at End of Period		0	2	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
Charged to Costs and Expenses		0
Charged to Other Accounts		0
Deductions		0
Balance at End of Period		0
Potomac Electric Power Company [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		17		21		29	17
Charged to Costs and Expenses				11		8	29
Charged to Other Accounts	[15]			3		2	3
Deductions	[16]			14		18	20
Balance at End of Period			29	21		21	29
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		1	0
Charged to Costs and Expenses				0		1	3
Charged to Other Accounts				0		0	0
Deductions				0		1	2
Balance at End of Period			1	1		1	1
Delmarva Power & Light Company [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		17		16		24	17
Charged to Costs and Expenses				6		3	23
Charged to Other Accounts	[17]			2		2	2
Deductions	[18]			11		13	18
Balance at End of Period			24	13		16	24
Delmarva Power & 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				0		1	1
Charged to Other Accounts				0		0	0
Deductions				0		1	1
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		18		27	17
Charged to Costs and Expenses				11		8	32
Charged to Other Accounts	[19]			2		2	2
Deductions	[20]			12		19	24
Balance at End of Period			27	19		18	27
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		1	0
Charged to Costs and Expenses				0		0	1
Charged to Other Accounts				0		0	0
Deductions				0		0	0
Balance at End of Period			$ 1	$ 1		$ 1	$ 1

[1] Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $13 million, $15 million, and $23 million for the years ended December 31, 2018, 2017 and 2016, 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 reflects the reclassification of assets as held for sale.

[6] Primarily reflects the reclassification of assets as held for sale.

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

[8] Write-off of individual accounts receivable.

[9] Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $13 million, $15 million, and $23 million for the years ended December 31, 2018, 2017, and 2016, respectively.

[10] Primarily charges for late payments.

[11] Write-off of individual accounts receivable.

[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.

[19] Primarily charges for late payments.

[20] Write-off of individual accounts receivable.