Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Notes payable—affiliated companies	$ 151	$ 151
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments, including money market funds	50	38
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments, including money market funds	0	0
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments, including money market funds	0	0
Carrying Amount [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Long-term debt (including $151 million of long-term notes payable to parent)	6,106	4,765
Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Long-term debt (including $151 million of long-term notes payable to parent)	$ 6,758	$ 5,345