Fair Value Measurements (Details) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Assets:
Cash equivalents	$ 185	$ 468
Available-for-sale securities	162	148
Interest rate derivatives	75	38
Foreign currency derivatives	8	0
Electricity commodity derivatives	1	0
Total assets	431	654
Liabilities:
Interest rate derivatives	68	24
Electricity commodity derivatives	1	1
Foreign currency derivatives	0	3
Total liabilities	69	28
Quoted Prices in Active Markets (Level 1) [Member]
Assets:
Cash equivalents	185	468
Available-for-sale securities	162	148
Interest rate derivatives	0	0
Foreign currency derivatives	0	0
Electricity commodity derivatives	0	0
Total assets	347	616
Quoted Prices in Active Markets (Level 1) [Member]
Liabilities:
Interest rate derivatives	0	0
Electricity commodity derivatives	0	0
Foreign currency derivatives	0	0
Total liabilities	0	0
Significant Other Observable Inputs (Level 2) [Member]
Assets:
Cash equivalents	0	0
Available-for-sale securities	0	0
Interest rate derivatives	75	38
Foreign currency derivatives	8	0
Electricity commodity derivatives	1	0
Total assets	84	38
Significant Other Observable Inputs (Level 2) [Member]
Liabilities:
Interest rate derivatives	68	24
Electricity commodity derivatives	1	1
Foreign currency derivatives	0	3
Total liabilities	69	28
Significant Unobservable Inputs (Level 3) [Member]
Assets:
Cash equivalents	0	0
Available-for-sale securities	0	0
Interest rate derivatives	0	0
Foreign currency derivatives	0	0
Electricity commodity derivatives	0	0
Total assets	0	0
Significant Unobservable Inputs (Level 3) [Member]
Liabilities:
Interest rate derivatives	0	0
Electricity commodity derivatives	0	0
Foreign currency derivatives	0	0
Total liabilities	$ 0	$ 0