Net Interest Revenue - Components of Interest Revenue and Interest Expenses (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Net Interest Revenue [Abstract]
Deposits with banks	$ 54	$ 34
U.S. Treasury and federal agencies	183	163
State and political subdivisions	58	71
Other investments	259	319
Securities purchased under resale agreements	11	9
Loans and leases	74	58
Other interest-earning assets	3	1
Total interest revenue	642	655
Deposits	26	15
Short-term borrowings	1	15
Long-term debt	62	63
Other interest-bearing liabilities	7	7
Total interest expense	96	100
Net interest revenue	$ 546	$ 555