Fair Value Measurements (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Carrying Amount [Member]
Fair Value Assets and Liabilities Measured on Recurring Basis Disclosure Items [Line Items]
Long-term debt, including current portion	$ 4,880	$ 5,052
Fair Value [Member]
Fair Value Assets and Liabilities Measured on Recurring Basis Disclosure Items [Line Items]
Long-term debt, including current portion	5,108	5,441
Fair Value, Inputs, Level 1 [Member]
Fair Value Assets and Liabilities Measured on Recurring Basis Disclosure Items [Line Items]
Investments, including money market funds	32	43
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