Fair value measurements (Details Textuals) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Fair value assets and liabilities measured on nonrecurring basis (Textual) [Line Items]
Loans measured at fair value on nonrecurring basis	$ 478,000,000	$ 664,000,000	$ 478,000,000	$ 664,000,000
Fair value measurements (Textuals) [Abstract]
Residential mortgage-backed securities at cost	1,200,000,000		1,200,000,000		1,500,000,000
Amount of available-for-sale investment securities derecognized due to adoption of new accounting rules		355,000,000		355,000,000
Number of independent pricing sources used to value privately issued residential mortgage backed securities valued with internal modeling	2		2
Privately issued residential mortgage - backed securities with internal modeling, at cost	1,200,000,000		1,200,000,000
Minimum range of Weightings applied to internal model valuations, in percentage			0.00%
Maximum range of Weightings applied to internal model valuations, in percentage			40.00%
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%
Fair value of privately issued residential mortgage-backed securities valued with internal modeling	1,400,000,000		1,400,000,000
Weighted-average market yield			7.60%
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	62,000,000		62,000,000		111,000,000
Change in fair value of nonrecurring fair value measured loans for charge-offs and impairment reserves	61,000,000	64,000,000	91,000,000	125,000,000
Assets taken in foreclosure of defaulted loans measured at fair value on a nonrecurring basis	50,000,000	127,000,000	50,000,000	127,000,000
Change in fair value of nonrecurring fair value measured foreclosed assets	13,000,000	16,000,000	15,000,000	21,000,000
Significant Observable Inputs (Level 2) [Member]
Fair value assets and liabilities measured on nonrecurring basis (Textual) [Line Items]
Loans measured at fair value on nonrecurring basis	324,000,000	378,000,000	324,000,000	378,000,000
Significant Unobservable Inputs (Level 3) [Member]
Fair value assets and liabilities measured on nonrecurring basis (Textual) [Line Items]
Loans measured at fair value on nonrecurring basis	$ 154,000,000	$ 286,000,000	$ 154,000,000	$ 286,000,000