Net Interest Revenue (Components of Interest Revenue and Interest Expenses) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Net Interest Revenue [Abstract]
Deposits with banks	$ 31	$ 35	$ 62	$ 77
U.S. Treasury and federal agencies	183	206	377	405
State and political subdivisions	54	54	105	108
Other investments	339	406	680	811
Securities purchased under resale agreements	12	13	25	22
Loans and leases	79	71	135	126
Other interest-earning assets	2	1	3	2
Total interest revenue	700	786	1,387	1,551
Deposits	27	37	61	90
Short-term borrowings	15	19	31	37
Long-term debt	54	54	110	120
Other interest-bearing liabilities	8	4	13	7
Total interest expense	104	114	215	254
Net interest revenue	$ 596	$ 672	$ 1,172	$ 1,297