Net Interest Revenue (Components of Interest Revenue and Interest Expenses) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Net Interest Revenue [Abstract]
Deposits with banks	$ 53	$ 29	$ 138	$ 91
U.S. Treasury and federal agencies	165	165	493	542
State and political subdivisions	58	59	173	164
Other investments	320	323	957	1,003
Securities purchased under resale agreements	9	8	27	33
Loans and leases	64	58	183	193
Other interest-earning assets	2	1	5	4
Total interest revenue	671	643	1,976	2,030
Deposits	33	17	66	78
Short-term borrowings	0	15	4	46
Long-term debt	60	59	186	169
Other interest-bearing liabilities	8	6	34	19
Total interest expense	101	97	290	312
Net interest revenue	$ 570	$ 546	$ 1,686	$ 1,718