Borrowings (Schedule of FHLB Advances, Disclosures) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Debt Disclosure [Abstract]
Maximum outstanding at any month end	$ 4,870	$ 2,646	$ 4,870	$ 3,557
Average outstanding balance	4,629	2,460	3,830	2,841
Average remaining borrowing capacity	$ 1,042	$ 983	$ 1,356	$ 843
Weighted average interest rate (as a percent)	1.22%	1.42%	1.20%	1.25%