Net Interest Revenue - Components of Interest Revenue and Interest Expenses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Net Interest Revenue [Abstract]
Deposits with banks	$ 54	$ 51	$ 108	$ 85
U.S. Treasury and federal agencies	176	164	359	327
State and political subdivisions	58	44	116	115
Other investments	247	318	506	637
Securities purchased under resale agreements	15	10	26	19
Loans and leases	77	61	151	119
Other interest-earning assets	2	2	5	3
Total interest revenue	629	650	1,271	1,305
Deposits	14	18	40	33
Short-term borrowings	3	(12)	3	3
Long-term debt	61	64	123	127
Other interest-bearing liabilities	16	19	24	26
Total interest expense	94	89	190	189
Net interest revenue	$ 535	$ 561	$ 1,081	$ 1,116