Related Party Transactions (Details) (USD $)	3 Months Ended			6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011	Jun. 30, 2012		Jun. 30, 2011	Dec. 31, 2011
Related Party Income Statement Activity [Abstract]
Total interest expense to affiliates, net	$ 6,000,000		$ 6,000,000	$ 12,000,000		$ 13,000,000
Total income (loss) in equity method investments				(79,000,000)
Cash dividends paid to parent				773,000,000		695,000,000
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	420,000,000			420,000,000			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	408,000,000		246,000,000	774,000,000		552,000,000
Operating and maintenance from affiliate	176,000,000		71,000,000	311,000,000		145,000,000
Total income (loss) in equity method investments				(79,000,000)
Cash distribution paid to member				891,000,000		0
Contributions from member				0		0
Related Party Balance Sheet [Abstract]
Mark-to-market derivative assets with affiliates	506,000,000	[1]		506,000,000	[1]		503,000,000	[2]
Total receivables from affiliates (current)	144,000,000			144,000,000			109,000,000
Mark-to-market derivative assets with affiliate (noncurrent assets)	0			0			191,000,000	[2]
Investments in affiliates	397,000,000			397,000,000			1,000,000
Total payables to affiliates (current)	115,000,000			115,000,000			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)	2,352,000,000			2,352,000,000			2,222,000,000
Commonwealth Edison Co [Member]
Related Party Income Statement Activity [Abstract]
Operating revenues from affiliates	1,000,000		0	1,000,000		1,000,000
Purchased power from affiliate	203,000,000		128,000,000	451,000,000		291,000,000
Operating and maintenance from affiliate	38,000,000		36,000,000	81,000,000		73,000,000
Total interest expense to affiliates, net	3,000,000		4,000,000	6,000,000		8,000,000
Cash dividends paid to parent				85,000,000		150,000,000
Contributions from parent				0		0
Related Party Balance Sheet [Abstract]
Total receivable from affiliates (noncurrent)	1,963,000,000			1,963,000,000			1,860,000,000
Investments in affiliates	6,000,000			6,000,000			6,000,000
Total payables to affiliates (current)	96,000,000			96,000,000			111,000,000
Mark-to-market derivative liabilities with affiliate (current liabilities)	506,000,000			506,000,000			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		0	2,000,000		2,000,000
Purchased power from affiliate	125,000,000		115,000,000	235,000,000		257,000,000
Operating and maintenance from affiliate	26,000,000		22,000,000	57,000,000		44,000,000
Total interest expense to affiliates, net	3,000,000		3,000,000	6,000,000		6,000,000
Cash dividends paid to parent				172,000,000		184,000,000
Contributions from parent				0		0
Repayment of receivable from parent				0		0
Related Party Balance Sheet [Abstract]
Total receivable from affiliates (noncurrent)	392,000,000			392,000,000			365,000,000
Investments in affiliates	8,000,000			8,000,000			8,000,000
Total payables to affiliates (current)	77,000,000			77,000,000			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	2,000,000		2,000,000	5,000,000		3,000,000
Operating and maintenance from affiliate	26,000,000		38,000,000	68,000,000		70,000,000
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 $233 million and $424 million, respectively, and current and noncurrent liabilities are shown inclusive of collateral of $(134) million and $(200) million, respectively. The total cash collateral received, net of cash collateral posted and offset against mark-to-market assets and liabilities was $323 million at June 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.