Fair value measurements (Details Textual) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011 Modification Investment Security	Sep. 30, 2010	Sep. 30, 2011 Modification Investment Security	Sep. 30, 2010	Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans measured at fair value on nonrecurring basis	$ 506,000,000	$ 625,000,000	$ 506,000,000	$ 625,000,000
Fair value measurements (Textual) [Abstract]
Number of independent pricing sources used to value privately issued residential mortgage backed securities valued with internal modeling	2		2
Residential mortgage-backed securities at cost	1,300,000,000		1,300,000,000		1,500,000,000
Weighted-average reliance on internal model pricing, in percentage			34.00%
Average weighting placed on the values provided by the independent sources, in percentage			66.00%
Privately issued residential mortgage - backed securities with internal modeling, at cost	1,300,000,000		1,300,000,000
Fair value of privately issued residential mortgage-backed securities valued with internal modeling	1,100,000,000		1,100,000,000
Weighted-average market yield			8.40%
Securities issued by financial institutions and other entities backed by trust preferred securities at cost	44,000,000		44,000,000		95,000,000
Fair value of securities issued by financial institutions and other entities backed by trust preferred securities	51,000,000		51,000,000		111,000,000
Amount of available-for-sale investment securities derecognized due to adoption of new accounting rules	355,000,000		355,000,000
Change in fair value of nonrecurring fair value measured loans for charge-offs and impairment reserves	38,000,000	61,000,000	137,000,000	154,000,000
Assets taken in foreclosure of defaulted loans measured at fair value on a nonrecurring basis	53,000,000	31,000,000	53,000,000	31,000,000
Change in fair value of nonrecurring fair value measured foreclosed assets	6,000,000	7,000,000	17,000,000	8,000,000
Carrying value of capitalized servicing rights	13,000,000	33,000,000	13,000,000	33,000,000
Increases (decreases) in fair value of capitalized servicing rights	1,000,000	3,000,000	1,000,000	6,000,000
Significant Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans measured at fair value on nonrecurring basis	355,000,000	373,000,000	355,000,000	373,000,000
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans measured at fair value on nonrecurring basis	$ 151,000,000	$ 252,000,000	$ 151,000,000	$ 252,000,000