Fair Value of Financial Instruments (Details) (USD $) In Millions	Sep. 30, 2011		Dec. 31, 2010		Sep. 30, 2010	Dec. 31, 2009
Assets:
Cash and cash equivalents	$ 1,127		$ 2,951		$ 3,447	$ 2,304
Funds deposited by counterparties	259		408
Restricted cash	441		8
Cash collateral paid in support of energy risk management activities	316		323
Investment in available-for-sale securities (classified within other non-current assets):
Derivative assets	3,121		2,722
Restricted cash supporting funded Letter of Credit facility	0		1,300
Liabilities
Long-term debt, including current portion	9,185		9,104
Funded letter of credit	0	[1]	1,300	[1]
Cash collateral received in support of energy risk management activities	259		408
Derivative liabilities	2,497		2,050
Carrying Amount
Assets:
Cash and cash equivalents	1,127		2,951
Funds deposited by counterparties	259		408
Restricted cash	441		8
Cash collateral paid in support of energy risk management activities	316		323
Investment in available-for-sale securities (classified within other non-current assets):
Debt securities	8		8
Marketable equity securities	1		3
Trust fund investments	401		414
Notes receivable	131		177
Derivative assets	3,121		2,722
Restricted cash supporting funded Letter of Credit facility	0		1,300
Liabilities
Long-term debt, including current portion	9,185		9,104
Funded letter of credit	0		1,300
Cash collateral received in support of energy risk management activities	259		408
Derivative liabilities	2,497		2,050
Fair Value
Assets:
Cash and cash equivalents	1,127		2,951
Funds deposited by counterparties	259		408
Restricted cash	441		8
Cash collateral paid in support of energy risk management activities	316		323
Investment in available-for-sale securities (classified within other non-current assets):
Debt securities	8		8
Marketable equity securities	1		3
Trust fund investments	401		414
Notes receivable	136		190
Derivative assets	3,121		2,722
Restricted cash supporting funded Letter of Credit facility	0		1,300
Liabilities
Long-term debt, including current portion	8,830		9,236
Funded letter of credit	0		1,295
Cash collateral received in support of energy risk management activities	259		408
Derivative liabilities	$ 2,497		$ 2,050

[1] On July 1, 2011, the Term loan facility, due 2013-2015 and Funded letter of credit were repaid and replaced, as described below under Senior Credit Facility.