Derivative Instruments and Hedging Activity - Fair Value of Derivative Instruments Included in Balance Sheets (Details) - Cash Flow Hedges [Member] - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Fair value of derivative instruments, assets	$ 18	$ 18
Fair value of derivative instruments, liabilities	50	46
Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative instruments, assets	10	1
Other Noncurrent Assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative instruments, assets	8	17
Current Derivative Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative instruments, liabilities	11	18
Other Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative instruments, liabilities	39	28
Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative instruments, assets	18	17
Fair value of derivative instruments, liabilities	47	46
Foreign Currency Contract [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative instruments, assets	0	1
Fair value of derivative instruments, liabilities	3	0
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative instruments, assets	15	16
Fair value of derivative instruments, liabilities	47	44
Not Designated as Hedging Instrument [Member] | Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative instruments, assets	15	15
Fair value of derivative instruments, liabilities	44	44
Not Designated as Hedging Instrument [Member] | Foreign Currency Contract [Member]
Derivatives, Fair Value [Line Items]
Fair value of derivative instruments, assets	0	1
Fair value of derivative instruments, liabilities	$ 3	$ 0