Fair Value Measurements and Credit Concentration (Assets and Liabilities Measured on Recurring Basis Table) (Details) (USD $) In Millions	Jun. 30, 2011		Dec. 31, 2010		Jun. 30, 2010	Dec. 31, 2009
Assets
Cash and cash equivalents	$ 1,269		$ 925		$ 4,505	$ 801
Short-term investments - municipal debt securities	0		163
Restricted cash and cash equivalents	88	[1]	66	[1]
Price risk management assets:
Energy commodities assets	2,113		2,503
Interest rate swaps assets	6		15
Foreign currency exchange contracts assets	4		11
Cross-currency swaps assets	9		44
Total Price risk management assets	2,132		2,573
NDT funds:
Cash and cash equivalents	10		10
Equity securities:
U.S. large-cap	304		303
U.S. mid/small-cap	124		119
Debt securities:
U.S. Treasury	79		75
U.S. government sponsored agency	10		7
Municipality	80		69
Investment-grade corporate	37		33
Other	3		1
Receivables (payables), net	1		1
Total NDT funds	648		618
Auction rate securities	25	[2]	25	[2]
Total assets	4,162		4,370
Price risk management liabilities:
Energy commodities liabilities	1,204		1,552
Interest rate swaps liabilities	51		53
Cross-currency swaps liabilities	5		9
Total Price risk management liabilities	1,260		1,614
Level 1 [Member]
Assets
Cash and cash equivalents	1,269		925
Short-term investments - municipal debt securities	0		163
Restricted cash and cash equivalents	88	[1]	66	[1]
Price risk management assets:
Energy commodities assets	3
Total Price risk management assets	3
NDT funds:
Cash and cash equivalents	10		10
Equity securities:
U.S. large-cap	211		207
U.S. mid/small-cap	91		89
Debt securities:
U.S. Treasury	79		75
Receivables (payables), net	(2)		(1)
Total NDT funds	389		380
Total assets	1,749		1,534
Price risk management liabilities:
Energy commodities liabilities	3
Total Price risk management liabilities	3
Level 2 [Member]
Price risk management assets:
Energy commodities assets	2,063		2,452
Interest rate swaps assets	6		15
Foreign currency exchange contracts assets	4		11
Cross-currency swaps assets	9		44
Total Price risk management assets	2,082		2,522
Equity securities:
U.S. large-cap	93		96
U.S. mid/small-cap	33		30
Debt securities:
U.S. government sponsored agency	10		7
Municipality	80		69
Investment-grade corporate	37		33
Other	3		1
Receivables (payables), net	3		2
Total NDT funds	259		238
Total assets	2,341		2,760
Price risk management liabilities:
Energy commodities liabilities	1,180		1,498
Interest rate swaps liabilities	51		53
Cross-currency swaps liabilities	5		9
Total Price risk management liabilities	1,236		1,560
Level 3 [Member]
Price risk management assets:
Energy commodities assets	47		51
Total Price risk management assets	47		51
Debt securities:
Auction rate securities	25	[2]	25	[2]
Total assets	72		76
Price risk management liabilities:
Energy commodities liabilities	21		54
Total Price risk management liabilities	$ 21		$ 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.