Segment information (Details 1) (USD $) In Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Summary of segment information
Average total assets	$ 72,489	$ 68,339	$ 68,380
Business Banking [Member]
Summary of segment information
Average total assets	4,995	4,850	4,843
Commercial Banking [Member]
Summary of segment information
Average total assets	17,397	15,460	15,461
Commercial Real Estate [Member]
Summary of segment information
Average total assets	14,730	13,198	13,194
Discretionary Portfolio [Member]
Summary of segment information
Average total assets	13,844	14,658	14,690
Residential Mortgage Banking [Member]
Summary of segment information
Average total assets	1,913	2,189	2,217
Retail Banking [Member]
Summary of segment information
Average total assets	11,904	12,133	12,079
All Other [Member]
Summary of segment information
Average total assets	$ 7,706	$ 5,851	$ 5,896