Schedule II - Valuation and Qualifying Accounts (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 272	[1]	$ 293	[1]	$ 199	[1]
Charged to Costs and Expenses	175	[1]	121	[1]	144	[1]
Charged to Other Accounts	69	[1]	37	[1],[2]	136	[1],[2],[3]
Deductions	205	[1],[4]	179	[1],[4]	186	[1],[4]
Balance at End of Period	311	[1]	272	[1]	293	[1]
Deferred Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	13		36		10
Charged to Costs and Expenses	0		1		18
Charged to Other Accounts	37		0		18	[3]
Deductions	0		24		10
Balance at End of Period	50		13		36
Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	58		53		60
Charged to Costs and Expenses	5		17		2
Charged to Other Accounts	34		0		2	[3]
Deductions	2		12		11
Balance at End of Period	95		58		53
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	57		84		29
Charged to Costs and Expenses	14		(16)		0
Charged to Other Accounts	8		0		66	[1]
Deductions	19		11		11
Balance at End of Period	60		57		84
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		35		0
Charged to Costs and Expenses	0		1		17
Charged to Other Accounts	37		0		18	[1]
Deductions	0		25		0
Balance at End of Period	48		11		35
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	55		50		59
Charged to Costs and Expenses	5		16		0
Charged to Other Accounts	32		0		2	[1]
Deductions	(1)		11		11
Balance at End of Period	93		55		50
Commonwealth Edison Co [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	62		70		78
Charged to Costs and Expenses	45		33		42
Charged to Other Accounts	33	[5]	29	[5]	26	[5]
Deductions	56	[4]	70	[4]	76	[4]
Balance at End of Period	84		62		70
Commonwealth Edison Co [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	2		2		1
Charged to Costs and Expenses	0		1		1
Charged to Other Accounts	2		0		0
Deductions	2		1		0
Balance at End of Period	2		2		2
PECO Energy Co [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Noncurrent portion of uncollectible installment plan receivables	8		9		8
PECO Energy Co [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	107	[1]	99	[1]	92	[1]
Charged to Costs and Expenses	52	[1]	61	[1]	60	[1]
Charged to Other Accounts	11	[1],[6]	7	[1],[6]	8	[1],[6]
Deductions	70	[1],[4]	60	[1],[4]	61	[1],[4]
Balance at End of Period	100	[1]	107	[1]	99	[1]
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
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
Baltimore Gas and Electric Company [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Charged to Costs and Expenses	19
Baltimore Gas and Electric Company [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	46		40		38
Charged to Costs and Expenses	64		43		45
Charged to Other Accounts	17	[6]	1		0
Deductions	60	[4]	38	[4]	43	[4]
Balance at End of Period	67		46		40
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		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
Baltimore Gas and Electric Company [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	1		1		0
Charged to Costs and Expenses	0		0		1
Charged to Other Accounts	0		0		0
Deductions	1		0		0
Balance at End of Period	$ 0		$ 1		$ 1

[1] Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $8 million, $9 million, and $8 million for the years ended December 31, 2014, 2013, and 2012, respectively.

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

[3] Primarily represents the addition of Constellation’s and BGE’s results as of March 12, 2012, the date of the merger.

[4] Write-off of individual accounts receivable.

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

[6] Primarily charges for late payments.