Loan Servicing (Commercial Mortgage Banking Activities) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Loan Servicing [Abstract]
Unpaid principal balance of commercial real estate mortgages serviced for others	$ 25,982	$ 25,367
Commercial real estate mortgages serviced for others covered by recourse provisions	4,847	4,520
Maximum recourse exposure from commercial real estate mortgages sold with recourse liability	1,327	1,226
Recorded reserves related to recourse exposure	14	15
Originated commercial real estate mortgages during the period - year to date	$ 3,342	$ 4,803