Net Interest Revenue - Components of Interest Revenue and Interest Expenses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Banking and Thrift [Abstract]
Deposits with banks	$ 29	$ 53	$ 101	$ 161
U.S. Treasury and federal agencies	200	178	620	537
State and political subdivisions	55	57	162	173
Other investments	208	227	580	733
Securities purchased under resale agreements	40	18	112	45
Trading account assets	0	0	1	0
Loans and leases	97	79	281	229
Other interest-earning assets	18	2	39	7
Total interest revenue	647	614	1,896	1,885
Deposits	20	28	73	67
Securities sold under repurchase agreements	0	0	1	0
Short-term borrowings	2	1	4	5
Long-term debt	68	62	191	185
Other interest-bearing liabilities	20	10	57	34
Total interest expense	110	101	326	291
Net interest revenue	$ 537	$ 513	$ 1,570	$ 1,594