Fair Value Measurements and Credit Concentration (Assets and Liabilities Measured on Recurring Basis Table) (Details) (USD $) In Millions	Sep. 30, 2011		Dec. 31, 2010		Sep. 30, 2010	Dec. 31, 2009
Assets
Cash and cash equivalents	$ 1,511		$ 925		$ 4,853	$ 801
Debt securities:
Total NDT funds	594		618
Recurring [Member]
Assets
Cash and cash equivalents	1,511		925
Short-term investments - municipal debt securities	0		163
Restricted cash and cash equivalents	117	[1]	66	[1]
Price risk management assets:
Energy commodities assets	2,042		2,503
Interest rate swaps assets	5		15
Foreign currency exchange contracts assets	21		11
Cross-currency swaps assets	51		44
Total price risk management assets	2,119		2,573
NDT funds:
Cash and cash equivalents	13		10
Equity securities:
U.S. large-cap	260		303
U.S. mid/small-cap	104		119
Debt securities:
U.S. Treasury	82		75
U.S. government sponsored agency	11		7
Municipality	82		69
Investment-grade corporate	37		33
Other	3		1
Receivables (payables), net	2		1
Total NDT funds	594		618
Auction rate securities	24	[2]	25	[2]
Total assets	4,365		4,370
Price risk management liabilities:
Energy commodities liabilities	1,191		1,552
Interest rate swaps liabilities	120		53
Cross-currency swaps liabilities	2		9
Total price risk management liabilities	1,313		1,614
Recurring [Member] | Level 1 [Member]
Assets
Cash and cash equivalents	1,511		925
Short-term investments - municipal debt securities	0		163
Restricted cash and cash equivalents	117	[1]	66	[1]
Price risk management assets:
Energy commodities assets	1		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	1		0
NDT funds:
Cash and cash equivalents	13		10
Equity securities:
U.S. large-cap	180		207
U.S. mid/small-cap	77		89
Debt securities:
U.S. Treasury	82		75
U.S. government sponsored agency	0		0
Municipality	0		0
Investment-grade corporate	0		0
Other	0		0
Receivables (payables), net	0		(1)
Total NDT funds	352		380
Auction rate securities	0		0
Total assets	1,981		1,534
Price risk management liabilities:
Energy commodities liabilities	1		0
Interest rate swaps 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	1,990		2,452
Interest rate swaps assets	5		15
Foreign currency exchange contracts assets	21		11
Cross-currency swaps assets	37		44
Total price risk management assets	2,053		2,522
NDT funds:
Cash and cash equivalents	0		0
Equity securities:
U.S. large-cap	80		96
U.S. mid/small-cap	27		30
Debt securities:
U.S. Treasury	0		0
U.S. government sponsored agency	11		7
Municipality	82		69
Investment-grade corporate	37		33
Other	3		1
Receivables (payables), net	2		2
Total NDT funds	242		238
Auction rate securities	0		0
Total assets	2,295		2,760
Price risk management liabilities:
Energy commodities liabilities	1,165		1,498
Interest rate swaps liabilities	120		53
Cross-currency swaps liabilities	2		9
Total price risk management liabilities	1,287		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	51		51
Interest rate swaps assets	0		0
Foreign currency exchange contracts assets	0		0
Cross-currency swaps assets	14		0
Total price risk management assets	65		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	89		76
Price risk management liabilities:
Energy commodities liabilities	25		54
Interest rate swaps liabilities	0		0
Cross-currency swaps liabilities	0		0
Total price risk management liabilities	$ 25		$ 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.