Related Party Transactions (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013		Dec. 31, 2013
Related Party Income Statement Activity [Abstract]
Purchased power from affiliate	$ 334		$ 318
Total interest expense to affiliates, net	10		6
Total income (loss) in equity method investments	(19)		(9)
Dividends paid on common stock	(266)		(450)
Related Party Balance Sheet [Abstract]
Investments in affiliates	22				22
Total payables to affiliates (current)	94				116
Equity Method Investment Summarized Financial Information[Abstract]
Amortization of energy contract assets and liabilities	42	[1]	176	[1]
Constellation Energy Nuclear Group [Member]
Schedule of Equity Method Investments [Line Items]
CENG	93		53
Amortization of basis difference in CENG	(88)		(131)
Total equity investment earnings (losses) - CENG	5		(78)
Exelon Generation Co L L C [Member]
Schedule of Equity Method Investments [Line Items]
Percentage of ownership interest in CENG (as a percent)	50.01%
Basis difference in investment in CENG	204
Related Party Income Statement Activity [Abstract]
Operating revenues from affiliates	334		392
Operating and maintenance from affiliate	149		147
Total interest expense to affiliates, net	12		17
Total income (loss) in equity method investments	(19)		(9)
Cash distribution paid to member	30		211
Contributions from member	0		0
Related Party Balance Sheet [Abstract]
Mark-to-market derivative assets with affiliates	0				0
Total receivables from affiliates (current)	122				108
Mark-to-market derivative assets with affiliate (noncurrent assets)	0				0
Investments in affiliates	0				0
Total payables to affiliates (current)	186				181
Total payables to affiliates (noncurrent)	2,773				2,740
Equity Method Investment Summarized Financial Information[Abstract]
Purchase of nuclear output by EDF (as a percent)	49.99%
Amortization of energy contract assets and liabilities	44	[1]	176	[1]
Exelon Generation Co L L C [Member] | Minimum [Member]
Equity Method Investment Summarized Financial Information[Abstract]
Required purchases of power from CENG's nuclear plants not sold to third parties (as a percent)	85.00%
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group [Member]
Schedule of Equity Method Investments [Line Items]
CENG	(2)		15
Amortization of basis difference in CENG	(17)		(27)
Total equity investment earnings (losses) - CENG	(19)		(12)
Commonwealth Edison Co [Member]
Related Party Income Statement Activity [Abstract]
Operating revenues from affiliates	1		1
Purchased power from affiliate	108		145
Operating and maintenance from affiliate	39		36
Total interest expense to affiliates, net	3		3
Dividends paid on common stock	(76)		(55)
Contributions from parent	38		0
Related Party Balance Sheet [Abstract]
Total receivable from affiliates (noncurrent)	2,497				2,469
Investments in affiliates	6				6
Total payables to affiliates (current)	63				83
Mark-to-market derivative liabilities with affiliate (current liabilities)	0				0
PECO Energy Co [Member]
Related Party Income Statement Activity [Abstract]
Operating revenues from affiliates	1		0
Purchased power from affiliate	87		141
Operating and maintenance from affiliate	24		24
Total interest expense to affiliates, net	3		3
Dividends paid on common stock	(80)		(83)
Related Party Balance Sheet [Abstract]
Total receivable from affiliates (noncurrent)	455				447
Investments in affiliates	8				8
Total payables to affiliates (current)	60				58
Baltimore Gas and Electric Company [Member]
Related Party Income Statement Activity [Abstract]
Operating revenues from affiliates	16		4
Purchased power from affiliate	120		113
Operating and maintenance from affiliate	25		19
Total interest expense to affiliates, net	4		4
Dividends paid on common stock	0		0
Contributions from parent	0		0
Related Party Balance Sheet [Abstract]
Investments in affiliates	8				8
Total payables to affiliates (current)	$ 59				$ 55

[1] Included in Operating revenues or Purchased power and fuel expense on the Registrants' Consolidated Statements of Operations and Comprehensive Income.