Net Interest Revenue - Components of Interest Revenue and Interest Expenses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Net Interest Revenue [Abstract]
Deposits with banks	$ 53	$ 53	$ 161	$ 138
U.S. Treasury and federal agencies	178	165	537	493
State and political subdivisions	57	58	173	173
Other investments	227	320	733	957
Securities purchased under resale agreements	18	9	45	27
Loans and leases	79	64	229	183
Other interest-earning assets	2	2	7	5
Total interest revenue	614	671	1,885	1,976
Deposits	28	33	67	66
Short-term borrowings	1	0	5	4
Long-term debt	62	60	185	186
Other interest-bearing liabilities	10	8	34	34
Total interest expense	101	101	291	290
Net interest revenue	$ 513	$ 570	$ 1,594	$ 1,686