Loans and Leases (Carrying Value of Purchased Impaired and Nonimpaired Loans) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Residential mortgage	$ 21,513	$ 20,581
Total covered	4,532	4,867
Other acquired	35	39
Purchased Impaired Loans [Member]
Residential mortgage	630	647
Commercial real estate	1,280	1,407
Commercial	58	68
Total covered	1,968	2,122
Other acquired	2	2
Total	1,970	2,124
Allowance for loan losses	(101)	(113)
Net	1,869	2,011
Purchased Nonimpaired Loans [Member]
Residential mortgage	582	617
Commercial real estate	1,495	1,597
Commercial	487	531
Total covered	2,564	2,745
Other acquired	33	37
Total	2,597	2,782
Allowance for loan losses	(36)	(36)
Net	2,561	2,746
Purchased Impaired and Nonimpaired Loans [Member]
Residential mortgage	1,212	1,264
Commercial real estate	2,775	3,004
Commercial	545	599
Total covered	4,532	4,867
Other acquired	35	39
Total	4,567	4,906
Allowance for loan losses	(137)	(149)
Net	$ 4,430	$ 4,757