Related Party Transactions (Details) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011	Sep. 30, 2012		Sep. 30, 2011	Dec. 31, 2011
Related Party Income Statement Activity [Abstract]
Total interest expense to affiliates, net	$ 6,000,000		$ 6,000,000	$ 19,000,000		$ 19,000,000
Total income (loss) in equity method investments				(69,000,000)
Cash dividends paid to parent				1,226,000,000		1,044,000,000
Related Party Balance Sheet [Abstract]
Mark-to-market derivative assets with affiliates	0			0			0
Mark-to-market derivative assets with affiliate (noncurrent assets)							0
Investments in affiliates	371,000,000			371,000,000			15,000,000
Mark-to-market derivative liabilities with affiliate (current liabilities)	0			0			0
Mark-to-market derivative liabilities with affiliate (noncurrent liabilities)							0
Exelon Generation Co L L C [Member]
Related Party Income Statement Activity [Abstract]
Operating revenues from affiliates	459,000,000		304,000,000	1,233,000,000		856,000,000
Operating and maintenance from affiliate	126,000,000		77,000,000	437,000,000		222,000,000
Total income (loss) in equity method investments				(69,000,000)
Cash distribution paid to member				1,384,000,000		61,000,000
Contributions from member				0		30,000,000
Related Party Balance Sheet [Abstract]
Mark-to-market derivative assets with affiliates	352,000,000	[1]		352,000,000	[1]		503,000,000	[2]
Total receivables from affiliates (current)	130,000,000			130,000,000			109,000,000
Mark-to-market derivative assets with affiliate (noncurrent assets)	0			0			191,000,000	[2]
Investments in affiliates	348,000,000			348,000,000			1,000,000
Total payables to affiliates (current)	99,000,000			99,000,000			58,000,000
Mark-to-market derivative liabilities with affiliate (current liabilities)	0			0			0
Mark-to-market derivative liabilities with affiliate (noncurrent liabilities)							0
Total payables to affiliates (noncurrent)	2,383,000,000			2,383,000,000			2,222,000,000
Commonwealth Edison Co [Member]
Related Party Income Statement Activity [Abstract]
Operating revenues from affiliates	0		1,000,000	2,000,000		2,000,000
Purchased power from affiliate	180,000,000		159,000,000	631,000,000		450,000,000
Operating and maintenance from affiliate	37,000,000		40,000,000	118,000,000		113,000,000
Total interest expense to affiliates, net	3,000,000		4,000,000	9,000,000		11,000,000
Cash dividends paid to parent				95,000,000		225,000,000
Contributions from parent				0		0
Related Party Balance Sheet [Abstract]
Total receivable from affiliates (noncurrent)	2,024,000,000			2,024,000,000			1,860,000,000
Investments in affiliates	6,000,000			6,000,000			6,000,000
Total payables to affiliates (current)	84,000,000			84,000,000			111,000,000
Mark-to-market derivative liabilities with affiliate (current liabilities)	352,000,000			352,000,000			503,000,000
Mark-to-market derivative liabilities with affiliate (noncurrent liabilities)	0			0			191,000,000
PECO Energy Co [Member]
Related Party Income Statement Activity [Abstract]
Operating revenues from affiliates	1,000,000		2,000,000	3,000,000		4,000,000
Purchased power from affiliate	171,000,000		137,000,000	407,000,000		394,000,000
Operating and maintenance from affiliate	27,000,000		24,000,000	83,000,000		68,000,000
Total interest expense to affiliates, net	3,000,000		3,000,000	9,000,000		9,000,000
Cash dividends paid to parent				258,000,000		268,000,000
Contributions from parent				0		18,000,000
Related Party Balance Sheet [Abstract]
Total receivable from affiliates (noncurrent)	362,000,000			362,000,000			365,000,000
Investments in affiliates	8,000,000			8,000,000			8,000,000
Total payables to affiliates (current)	76,000,000			76,000,000			62,000,000
Mark-to-market derivative liabilities with affiliate (current liabilities)	0			0			0
Baltimore Gas and Electric Company [Member]
Related Party Income Statement Activity [Abstract]
Operating revenues from affiliates	4,000,000		3,000,000	9,000,000		6,000,000
Operating and maintenance from affiliate	29,000,000		26,000,000	97,000,000		96,000,000
Total interest expense to affiliates, net	0		0	0		0
Cash dividends paid to parent				0		85,000,000
Contributions from parent				66,000,000
Related Party Balance Sheet [Abstract]
Investments in affiliates	8,000,000			8,000,000			8,000,000
Total payables to affiliates (current)	$ 44,000,000			$ 44,000,000			$ 41,000,000

[1] Current and noncurrent assets are shown net of collateral of $92 million and $263 million, respectively, and current and noncurrent liabilities are shown net of collateral of $(49) million and $(113) million, respectively. The total cash collateral received, net of cash collateral posted and offset against mark-to-market assets and liabilities was $193 million at September 30, 2012.

[2] Current and noncurrent assets are shown net of collateral of $338 million and $187 million, respectively, and current and noncurrent liabilities are shown inclusive of collateral of $15 million and $0 million, respectively. The total cash collateral received net of cash collateral posted and offset against mark-to-market assets and liabilities was $540 million at December 31, 2011.