Commitments and Contingencies Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Minimum lease obligations [Abstract]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	$ 135
Operating Leases, Future Minimum Payments, Due in Two Years	96
Operating Leases, Future Minimum Payments, Due in Three Years	65
Operating Leases, Future Minimum Payments, Due in Four Years	49
Operating Leases, Future Minimum Payments, Due in Five Years	41
Operating Leases, Rent Expense	$ 144	$ 132	$ 148