Fair Value Measurements (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Investments, including money market funds	$ 34	$ 43
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	4,742	5,052
Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Long-term debt	$ 5,059	$ 5,441