Net Interest Revenue - Components of Interest Revenue and Interest Expenses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Banking and Thrift [Abstract]
Deposits with banks	$ 208	$ 196	$ 125
U.S. Treasury and federal agencies	735	672	707
State and political subdivisions	227	231	249
Other investments	934	1,241	1,331
Securities purchased under resale agreements	62	38	45
Loans and leases	311	266	253
Other interest-earning assets	11	8	4
Total interest revenue	2,488	2,652	2,714
Deposits	97	99	93
Short-term borrowings	7	5	60
Long-term debt	250	245	232
Other interest-bearing liabilities	46	43	26
Total interest expense	400	392	411
Net interest revenue	$ 2,088	$ 2,260	$ 2,303