Net Interest Revenue - Components of Interest Revenue and Interest Expenses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Banking and Thrift [Abstract]
Deposits with banks	$ 43	$ 54
U.S. Treasury and federal agencies	211	183
State and political subdivisions	52	58
Other investments	183	259
Securities purchased under resale agreements	36	11
Loans and leases	91	74
Other interest-earning assets	13	3
Total interest revenue	629	642
Deposits	38	26
Short-term borrowings	0	1
Long-term debt	61	62
Other interest-bearing liabilities	18	7
Total interest expense	117	96
Net interest revenue	$ 512	$ 546