Related Party Transactions (Details) (USD $)	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011	Dec. 31, 2011
Related Party Income Statement Activity [Abstract]
Purchased power from affiliate	$ 0		$ 0
Total interest expense to affiliates, net	6,000,000		6,000,000
Cash dividends paid to parent	350,000,000		348,000,000
Related Party Balance Sheet [Abstract]
Mark-to-market derivative assets with affiliates	0			0
Mark-to-market derivative assets with affiliate (noncurrent assets)	0			0
Investments in affiliates	362,000,000			15,000,000
Mark-to-market derivative liabilities with affiliate (current liabilities)	0			0
Mark-to-market derivative liabilities with affiliate (noncurrent liabilities)	0			0
Exelon Generation Co L L C [Member]
Related Party Income Statement Activity [Abstract]
Operating revenues from affiliates	366,000,000		306,000,000
Operating and maintenance from affiliate	136,000,000		74,000,000
Cash distribution paid to member	600,000,000		0
Contributions from member	0		0
Related Party Balance Sheet [Abstract]
Mark-to-market derivative assets with affiliates	590,000,000	[1]		503,000,000	[2]
Total receivables from affiliates (current)	142,000,000			109,000,000
Mark-to-market derivative assets with affiliate (noncurrent assets)	92,000,000	[1]		191,000,000	[2]
Investments in affiliates	340,000,000			1,000,000
Total payables to affiliates (current)	183,000,000			58,000,000
Mark-to-market derivative liabilities with affiliate (current liabilities)	0			0
Mark-to-market derivative liabilities with affiliate (noncurrent liabilities)	0			0
Total payables to affiliates (noncurrent)	2,430,000,000			2,222,000,000
Commonwealth Edison Co [Member]
Related Party Income Statement Activity [Abstract]
Operating revenues from affiliates	1,000,000		1,000,000
Purchased power from affiliate	247,000,000		163,000,000
Operating and maintenance from affiliate	42,000,000		37,000,000
Total interest expense to affiliates, net	3,000,000		3,000,000
Cash dividends paid to parent	75,000,000		75,000,000
Contributions from parent	0		0
Related Party Balance Sheet [Abstract]
Total receivable from affiliates (noncurrent)	2,020,000,000			1,860,000,000
Investments in affiliates	6,000,000			6,000,000
Total payables to affiliates (current)	125,000,000			111,000,000
Mark-to-market derivative liabilities with affiliate (current liabilities)	590,000,000			503,000,000
Mark-to-market derivative liabilities with affiliate (noncurrent liabilities)	92,000,000			191,000,000
PECO Energy Co [Member]
Related Party Income Statement Activity [Abstract]
Operating revenues from affiliates	1,000,000		1,000,000
Purchased power from affiliate	111,000,000		141,000,000
Operating and maintenance from affiliate	30,000,000		22,000,000
Total interest expense to affiliates, net	3,000,000		3,000,000
Cash dividends paid to parent	87,000,000		111,000,000
Contributions from parent	0		0
Repayment of receivable from parent	0		0
Related Party Balance Sheet [Abstract]
Total receivable from affiliates (noncurrent)	413,000,000			365,000,000
Investments in affiliates	8,000,000			8,000,000
Total payables to affiliates (current)	75,000,000			62,000,000
Mark-to-market derivative liabilities with affiliate (current liabilities)	0			0
Baltimore Gas and Electric Company [Member]
Related Party Income Statement Activity [Abstract]
Operating revenues from affiliates	3,000,000		1,000,000
Purchased power from affiliate	92,000,000		57,000,000
Operating and maintenance from affiliate	42,000,000		32,000,000
Total interest expense to affiliates, net	0		0
Cash dividends paid to parent			85,000,000
Related Party Balance Sheet [Abstract]
Investments in affiliates	8,000,000			8,000,000
Total payables to affiliates (current)	$ 102,000,000			$ 41,000,000

[1] Current and noncurrent assets are shown net of collateral of $281 million and $400 million, respectively, and current and noncurrent liabilities are shown inclusive of collateral of $(212) million and $(231) million, respectively. The total cash collateral received, net of cash collateral posted and offset against mark-to-market assets and liabilities was $238 million at March 31, 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.