Guarantees and Commitments (Schedule of Lease Commitments) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Guarantees and Commitments [Abstract]
Operating leases, future minimum payments due, next twelve months	$ 48
Operating leases, future minimum payments, due in two years	47
Operating leases, future minimum payments, due in three years	46
Operating leases, future minimum payments, due in four years	37
Operating leases, future minimum payments, due in five years	31
Operating leases, future minimum payments, due thereafter	294
Total future minimum payments due, operating leases	503
Operating leases, rent expense	$ 45	$ 46	$ 51