Use of Collateral (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Use of Collateral [Abstract]
Margin deposits	$ 262	[1]	$ 140	[1]
Natural gas and power prepayments	37		42
Total margin deposits and natural gas and power prepayments with our counterparties	299	[2]	182	[2]
Letters of credit issued	561		581
First priority liens under power and natural gas agreements	1		1
First priority liens under interest rate swap agreements	203		318
Total letters of credit and first priority liens with our counterparties	765		900
Margin deposits held by us posted by our counterparties	45	[1],[3]	34	[1],[3]
Letters of credit posted with us by our counterparties	1		0
Total margin deposits and letters of credit posted with us by our counterparties	46		34
Use of Collateral (Textuals) [Abstract]
Margin And Prepayment Amounts Included In Other Assets	24		20
Margin And Prepayment Amounts Included In Margin Deposits And Other Prepaid Expenses	$ 275		$ 162

[1] Balances are subject to master netting arrangements and presented on a gross basis on our Consolidated Condensed Balance Sheets. We do not offset fair value amounts recognized for derivative instruments executed with the same counterparty under a master netting arrangement for financial statement presentation.

[2] At June 30, 2012 and December 31, 2011, $275 million and $162 million, respectively, were included in margin deposits and other prepaid expense and $24 million and $20 million, respectively, were included in other assets on our Consolidated Condensed Balance Sheets.

[3] Included in other current liabilities on our Consolidated Condensed Balance Sheets.