Changes in Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	$ (32)	$ (79)	$ (54)
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges and Treasury Locks, Effect Net of Tax	1	107	152
Unrealized gain (loss) on available-for-sale securities	(1)	(6)	0
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	(27)	(21)	(10)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(59)	1	88
Cumulative Translation Adjustment, Net of Tax, Period Increase (Decrease)	48	(25)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Before Reclassifications, Net of Tax		40
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax	(10)	(6)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, before Reclassification Adjustments, Net of Tax	(8)	(17)
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost Recognized in Net Periodic Pension Cost, Net of Tax	2	6
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	6	11	(27)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(35)	(8)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Reclassified from OCI, Net of Tax		(85)
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax	15	0
Other Comprehensive Income (Loss), Reclassifications out of OCI, Net of Tax	(25)	(79)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	48	(25)	(16)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	(106)	(45)	(67)
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, before Reclassification Adjustments and Tax	5	(6)	0
Other Comprehensive Income (Loss), Net of Tax	(59)	(87)	(56)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising Reclassed from OCI, Tax	$ 0	$ 0	$ 1