Net Interest Revenue - Components of Interest Revenue and Interest Expenses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Banking and Thrift [Abstract]
Deposits with banks	$ 126	$ 208	$ 196
U.S. Treasury and federal agencies	821	735	672
State and political subdivisions	224	227	231
Other investments	756	934	1,241
Securities purchased under resale agreements	146	62	38
Loans and leases	378	311	266
Other interest-earning assets	61	11	8
Total interest revenue	2,512	2,488	2,652
Deposits	85	97	99
Securities sold under repurchase agreements	1	0	0
Short-term borrowings	7	7	5
Long-term debt	260	250	245
Other interest-bearing liabilities	75	46	43
Total interest expense	428	400	392
Net interest revenue	$ 2,084	$ 2,088	$ 2,260