Fair Value Measurements and Credit Concentration (Assets and Liabilities Measured on Recurring Basis Table) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011		Mar. 31, 2011	Dec. 31, 2010
Assets
Cash and cash equivalents	$ 1,103		$ 1,202		$ 1,245	$ 925
Debt securities:
Total NDT funds	693		640
Recurring [Member]
Assets
Cash and cash equivalents	1,103		1,202
Restricted cash and cash equivalents	230	[1]	209	[1]
Price risk management assets:
Energy commodities assets	4,371		3,423
Interest rate swaps assets	3		3
Foreign currency contracts assets	5		18
Cross-currency swaps assets	37		24
Total price risk management assets	4,416		3,468
NDT funds:
Cash and cash equivalents	8		12
Equity Securities (Numeric) [Abstract]
U.S. large-cap	329		292
U.S. mid/small-cap	133		117
Debt securities:
U.S. Treasury	87		86
U.S. government sponsored agency	10		10
Municipality	84		83
Investment-grade corporate	38		38
Other	2		2
Receivables (payables), net	2		0
Total NDT funds	693		640
Auction rate securities	24	[2]	24	[2]
Total assets	6,466		5,543
Price risk management liabilities:
Energy commodities liabilities	3,154		2,345
Interest rate swaps liabilities	54		63
Foreign currency contracts liabilities	13		0
Cross-currency swaps liabilities	2		2
Total price risk management liabilities	3,223		2,410
Recurring [Member] | Level 1 [Member]
Assets
Cash and cash equivalents	1,103		1,202
Restricted cash and cash equivalents	230	[1]	209	[1]
Price risk management assets:
Energy commodities assets	2		3
Interest rate swaps assets	0		0
Foreign currency contracts assets	0		0
Cross-currency swaps assets	0		0
Total price risk management assets	2		3
NDT funds:
Cash and cash equivalents	8		12
Equity Securities (Numeric) [Abstract]
U.S. large-cap	228		202
U.S. mid/small-cap	98		87
Debt securities:
U.S. Treasury	87		86
U.S. government sponsored agency	0		0
Municipality	0		0
Investment-grade corporate	0		0
Other	0		0
Receivables (payables), net	0		(3)
Total NDT funds	421		384
Auction rate securities	0		0
Total assets	1,756		1,798
Price risk management liabilities:
Energy commodities liabilities	2		1
Interest rate swaps liabilities	0		0
Foreign currency contracts liabilities	0		0
Cross-currency swaps liabilities	0		0
Total price risk management liabilities	2		1
Recurring [Member] | Level 2 [Member]
Assets
Cash and cash equivalents	0		0
Restricted cash and cash equivalents	0		0
Price risk management assets:
Energy commodities assets	4,336		3,390
Interest rate swaps assets	3		3
Foreign currency contracts assets	5		18
Cross-currency swaps assets	34		20
Total price risk management assets	4,378		3,431
NDT funds:
Cash and cash equivalents	0		0
Equity Securities (Numeric) [Abstract]
U.S. large-cap	101		90
U.S. mid/small-cap	35		30
Debt securities:
U.S. Treasury	0		0
U.S. government sponsored agency	10		10
Municipality	84		83
Investment-grade corporate	38		38
Other	2		2
Receivables (payables), net	2		3
Total NDT funds	272		256
Auction rate securities	0		0
Total assets	4,650		3,687
Price risk management liabilities:
Energy commodities liabilities	3,138		2,327
Interest rate swaps liabilities	54		63
Foreign currency contracts liabilities	13		0
Cross-currency swaps liabilities	2		2
Total price risk management liabilities	3,207		2,392
Recurring [Member] | Level 3 [Member]
Assets
Cash and cash equivalents	0		0
Restricted cash and cash equivalents	0		0
Price risk management assets:
Energy commodities assets	33		30
Interest rate swaps assets	0		0
Foreign currency contracts assets	0		0
Cross-currency swaps assets	3		4
Total price risk management assets	36		34
NDT funds:
Cash and cash equivalents	0		0
Equity Securities (Numeric) [Abstract]
U.S. large-cap	0		0
U.S. mid/small-cap	0		0
Debt securities:
U.S. Treasury	0		0
U.S. government sponsored agency	0		0
Municipality	0		0
Investment-grade corporate	0		0
Other	0		0
Receivables (payables), net	0		0
Total NDT funds	0		0
Auction rate securities	24	[2]	24	[2]
Total assets	60		58
Price risk management liabilities:
Energy commodities liabilities	14		17
Interest rate swaps liabilities	0		0
Foreign currency contracts liabilities	0		0
Cross-currency swaps liabilities	0		0
Total price risk management liabilities	$ 14		$ 17

[1] Current portion is included in "Restricted cash and cash equivalents" and long-term portion is included in "Other noncurrent assets" on the Balance Sheets.

[2] Included in "Other investments" on the Balance Sheets.