Net Interest Revenue (Components of Interest Revenue and Interest Expenses) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Net Interest Revenue [Abstract]
Deposits with banks	$ 34	$ 31
U.S. Treasury and federal agencies	163	194
State and political subdivisions	71	51
Other investments	319	341
Securities purchased under resale agreements	9	13
Loans and leases	58	56
Other interest-earning assets	1	1
Total interest revenue	655	687
Deposits	15	34
Short-term borrowings	15	16
Long-term debt	63	56
Other interest-bearing liabilities	7	5
Total interest expense	100	111
Net interest revenue	$ 555	$ 576