Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	[1]	$ 311		$ 272		$ 293
Charged to Costs and Expenses	[1]	113		175		121
Charged to Other Accounts	[1]	27		69	[2]	37	[2],[3]
Deductions	[1],[4]	167		205		179
Balance at End of Period	[1]	284		311		272
Deferred Tax Valuation Allowance [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		50		13		36
Charged to Costs and Expenses		0		0		1
Charged to Other Accounts		(27)		37		0	[3]
Deductions		10		0		24
Balance at End of Period		13		50		13
Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		95		58		53
Charged to Costs and Expenses		10		5		17
Charged to Other Accounts		2		34		0	[3]
Deductions		2		2		12
Balance at End of Period		105		95		58
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		60		57		84
Charged to Costs and Expenses		22		14		(16)
Charged to Other Accounts		0		8		0	[1]
Deductions		5		19		11
Balance at End of Period		77		60		57
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		48		11		35
Charged to Costs and Expenses		0		0		1
Charged to Other Accounts		(27)		37		0
Deductions		10		0		25
Balance at End of Period		11		48		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		93		55		50
Charged to Costs and Expenses		9		5		16
Charged to Other Accounts		0		32		0	[1]
Deductions		0		(1)		11
Balance at End of Period		102		93		55
Commonwealth Edison Co [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		84		62		70
Charged to Costs and Expenses		39		45		33
Charged to Other Accounts	[5]	18		33		29
Deductions	[6]	66		56		70
Balance at End of Period		75		84		62
Commonwealth Edison Co [Member] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		2		2		2
Charged to Costs and Expenses		1		0		1
Charged to Other Accounts		2		2		0
Deductions		2		2		1
Balance at End of Period		3		2		2
PECO Energy Co [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Noncurrent portion of uncollectible installment plan receivables		8		8		9
PECO Energy Co [Member] | Allowance for Uncollectible Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	[7]	100		107		99
Charged to Costs and Expenses	[7]	37		52		61
Charged to Other Accounts	[7],[8]	9		11		7
Deductions	[7],[9]	63		70		60
Balance at End of Period	[7]	83		100		107
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		67		46		40
Charged to Costs and Expenses		15		64		43
Charged to Other Accounts		0	[10]	17		1
Deductions	[11]	33		60		38
Balance at End of Period		49		67		46
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		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] | Reserve for Obsolete Materials [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period		0		1		0
Charged to Costs and Expenses		0		0		0
Charged to Other Accounts		0		0		0
Deductions		0		1		0
Balance at End of Period		$ 0		$ 0		$ 1

[1] Excludes the non-current allowance for uncollectible accounts related to PECO’s installment plan receivables of $8 million, $8 million, and $9 million for the years ended December 31, 2015, 2014, and 2013, respectively.

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

[3] .

[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 $8 million, $8 million, and $9 million for the years ended December 31, 2015, 2014, and 2013, 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.