Net Interest Revenue - Components of Interest Revenue and Interest Expenses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Banking and Thrift [Abstract]
Deposits with banks	$ 30	$ 54	$ 73	$ 108
U.S. Treasury and federal agencies	209	176	420	359
State and political subdivisions	54	58	108	116
Other investments	189	247	371	506
Securities purchased under resale agreements	35	15	71	26
Loans and leases	93	77	184	151
Other interest-earning assets	10	2	22	5
Total interest revenue	620	629	1,249	1,271
Deposits	16	14	54	40
Interest Expense, Securities Sold under Agreements to Repurchase	0	0	1	0
Short-term borrowings	2	3	2	3
Long-term debt	62	61	122	123
Other interest-bearing liabilities	19	16	37	24
Total interest expense	99	94	216	190
Net interest revenue	$ 521	$ 535	$ 1,033	$ 1,081