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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Net Interest Revenue [Abstract]
Deposits with banks	$ 29	$ 31	$ 91	$ 108
U.S. Treasury and federal agencies	165	200	542	605
State and political subdivisions	59	53	164	161
Other investments	323	374	1,003	1,185
Securities purchased under resale agreements	8	15	33	37
Loans and leases	58	57	193	183
Other interest-earning assets	1	0	4	2
Total interest revenue	643	730	2,030	2,281
Deposits	17	37	78	127
Short-term borrowings	15	18	46	55
Long-term debt	59	52	169	172
Other interest-bearing liabilities	6	4	19	11
Total interest expense	97	111	312	365
Net interest revenue	$ 546	$ 619	$ 1,718	$ 1,916