Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Carrying Amount [Member]
Fair Value Assets and Liabilities Measured on Recurring Basis Disclosure Items [Line Items]
Long-term debt, including current portion	$ 5,052	$ 4,995
Fair Value [Member]
Fair Value Assets and Liabilities Measured on Recurring Basis Disclosure Items [Line Items]
Long-term debt, including current portion	5,441	5,165
Fair Value, Inputs, Level 1 [Member]
Fair Value Assets and Liabilities Measured on Recurring Basis Disclosure Items [Line Items]
Investments, including money market funds	43	38
Fair Value, Inputs, Level 2 [Member]
Fair Value Assets and Liabilities Measured on Recurring Basis Disclosure Items [Line Items]
Assets or liabilities	0	0
Fair Value, Inputs, Level 3 [Member]
Fair Value Assets and Liabilities Measured on Recurring Basis Disclosure Items [Line Items]
Assets or liabilities	$ 0	$ 0