Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Assets:
Cash equivalents	$ 91	$ 120
Available-for-sale securities	167	179
Interest rate derivatives	70	73
Electricity commodity derivatives	6	5
Total assets	334	377
Liabilities:
Interest rate derivatives	69	74
Foreign currency derivatives	7	2
Total liabilities	76	76
Significant Other Observable Inputs (Level 2) [Member]
Liabilities:
Interest rate derivatives	69	74
Foreign currency derivatives	7	2
Total liabilities	76	76
Significant Unobservable Inputs (Level 3) [Member]
Liabilities:
Interest rate derivatives
Foreign currency derivatives
Total liabilities
Quoted Prices in Active Markets (Level 1) [Member]
Assets:
Cash equivalents	91	120
Available-for-sale securities	142	154
Total assets	233	274
Significant Other Observable Inputs (Level 2) [Member]
Assets:
Interest rate derivatives	70	73
Electricity commodity derivatives	6	5
Total assets	76	78
Significant Unobservable Inputs (Level 3) [Member]
Assets:
Cash equivalents
Available-for-sale securities	25	25
Interest rate derivatives
Electricity commodity derivatives
Total assets	$ 25	$ 25