Guarantees and Commitments Guarantees and Commitments (Schedule of Lease Commitments) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Guarantees [Abstract]
Operating Leases, Rent Expense	$ 51	$ 51	$ 50
Operating Leases, Future Minimum Payments Due, Next Twelve Months	36
Operating Leases, Future Minimum Payments, Due in Two Years	36
Operating Leases, Future Minimum Payments, Due in Three Years	35
Operating Leases, Future Minimum Payments, Due in Four Years	33
Operating Leases, Future Minimum Payments, Due in Five Years	25
Operating Leases, Future Minimum Payments, Due Thereafter	75
Operating Leases, Rent Expense	$ 240