Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Leases [Abstract]
Rent Expense, Net	$ 88	$ 80	$ 76
Leases, Future Minimum Payments Due, Next Twelve Months	72
Leases, Future Minimum Payments, Due in Two Years	52
Operating Leases, Future Minimum Payments, Due in Three Years	40
Leases, Future Minimum Payments, Due in Four Years	33
Leases, Future Minimum Payments, Due in Five Years	28
Leases, Future Minimum Payments, Due Thereafter	93
Leases, Future Minimum Payments Due	317
Purchase Obligations, Future Minimum Payments Due, Current	262
Purchase Obligations, Future Minimum Payments, Due in Two Years	26
Purchase Obligations, Future Minimum Payments, Due in Three Years	15
Purchase Obligations, Future Minimum Payments, Due in Four Years	13
Purchase Obligations, Future Minimum Payments, Due in Five Years	5
Purchase Obligations, Future Minimum Payments, Due Thereafter	6
Purchase Obligations, Future Minimum Payments Due	$ 327