Fair Value Measurements and Credit Concentration (Assets and Liabilities Measured on Recurring Basis Table) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009	Dec. 31, 2008
Assets
Cash and cash equivalents	$ 1,202		$ 925		$ 801	$ 1,100
Debt securities:
Total NDT funds	640		618
Recurring [Member]
Assets
Cash and cash equivalents	1,202		925
Short-term investments - municipal debt securities	0		163
Restricted cash and cash equivalents	209	[1]	66	[1]
Price risk management assets:
Energy commodities assets	3,423		2,503
Interest rate swaps assets	3		15
Foreign currency exchange contracts assets	18		11
Cross-currency swaps assets	24		44
Total price risk management assets	3,468		2,573
NDT funds:
Cash and cash equivalents	12		10
Equity securities:
U.S. large-cap	292		303
U.S. mid/small-cap	117		119
Debt securities:
U.S. Treasury	86		75
U.S. government sponsored agency	10		7
Municipality	83		69
Investment-grade corporate	38		33
Other	2		1
Receivables (payables), net	0		1
Total NDT funds	640		618
Auction rate securities	24	[2]	25	[2]
Total assets	5,543		4,370
Price risk management liabilities:
Energy commodities liabilities	2,345		1,552
Interest rate swaps liabilities	63		53
Foreign currency exchange contracts liabilities	0		0
Cross-currency swaps liabilities	2		9
Total price risk management liabilities	2,410		1,614
Recurring [Member] | Level 1 [Member]
Assets
Cash and cash equivalents	1,202		925
Short-term investments - municipal debt securities	0		163
Restricted cash and cash equivalents	209	[1]	66	[1]
Price risk management assets:
Energy commodities assets	3		0
Interest rate swaps assets	0		0
Foreign currency exchange contracts assets	0		0
Cross-currency swaps assets	0		0
Total price risk management assets	3		0
NDT funds:
Cash and cash equivalents	12		10
Equity securities:
U.S. large-cap	202		207
U.S. mid/small-cap	87		89
Debt securities:
U.S. Treasury	86		75
U.S. government sponsored agency	0		0
Municipality	0		0
Investment-grade corporate	0		0
Other	0		0
Receivables (payables), net	(3)		(1)
Total NDT funds	384		380
Auction rate securities	0		0
Total assets	1,798		1,534
Price risk management liabilities:
Energy commodities liabilities	1		0
Interest rate swaps liabilities	0		0
Foreign currency exchange contracts liabilities	0		0
Cross-currency swaps liabilities	0		0
Total price risk management liabilities	1		0
Recurring [Member] | Level 2 [Member]
Assets
Cash and cash equivalents	0		0
Short-term investments - municipal debt securities	0		0
Restricted cash and cash equivalents	0		0
Price risk management assets:
Energy commodities assets	3,390		2,452
Interest rate swaps assets	3		15
Foreign currency exchange contracts assets	18		11
Cross-currency swaps assets	20		44
Total price risk management assets	3,431		2,522
NDT funds:
Cash and cash equivalents	0		0
Equity securities:
U.S. large-cap	90		96
U.S. mid/small-cap	30		30
Debt securities:
U.S. Treasury	0		0
U.S. government sponsored agency	10		7
Municipality	83		69
Investment-grade corporate	38		33
Other	2		1
Receivables (payables), net	3		2
Total NDT funds	256		238
Auction rate securities	0		0
Total assets	3,687		2,760
Price risk management liabilities:
Energy commodities liabilities	2,327		1,498
Interest rate swaps liabilities	63		53
Foreign currency exchange contracts liabilities	0		0
Cross-currency swaps liabilities	2		9
Total price risk management liabilities	2,392		1,560
Recurring [Member] | Level 3 [Member]
Assets
Cash and cash equivalents	0		0
Short-term investments - municipal debt securities	0		0
Restricted cash and cash equivalents	0		0
Price risk management assets:
Energy commodities assets	30		51
Interest rate swaps assets	0		0
Foreign currency exchange contracts assets	0		0
Cross-currency swaps assets	4		0
Total price risk management assets	34		51
NDT funds:
Cash and cash equivalents	0		0
Equity securities:
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]	25	[2]
Total assets	58		76
Price risk management liabilities:
Energy commodities liabilities	17		54
Interest rate swaps liabilities	0		0
Foreign currency exchange contracts liabilities	0		0
Cross-currency swaps liabilities	0		0
Total price risk management liabilities	$ 17		$ 54

[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.