Fair Value Measurements (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Assets:
Cash equivalents	$ 326	$ 468
Available-for-sale securities	142	148
Interest rate derivatives	50	38
Total assets	518	654
Liabilities:
Electricity commodity derivatives	2	1
Interest rate derivatives	22	24
Foreign currency derivatives	17	3
Total liabilities	41	28
Quoted Prices in Active Markets (Level 1) [Member]
Assets:
Cash equivalents	326	468
Available-for-sale securities	142	148
Interest rate derivatives	0	0
Total assets	468	616
Quoted Prices in Active Markets (Level 1) [Member]
Liabilities:
Electricity commodity derivatives	0	0
Interest rate 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	50	38
Total assets	50	38
Significant Other Observable Inputs (Level 2) [Member]
Liabilities:
Electricity commodity derivatives	2	1
Interest rate derivatives	22	24
Foreign currency derivatives	17	3
Total liabilities	41	28
Significant Unobservable Inputs (Level 3) [Member]
Assets:
Cash equivalents	0	0
Available-for-sale securities	0	0
Interest rate derivatives	0	0
Total assets	0	0
Significant Unobservable Inputs (Level 3) [Member]
Liabilities:
Electricity commodity derivatives	0	0
Interest rate derivatives	0	0
Foreign currency derivatives	0	0
Total liabilities	$ 0	$ 0