Transfers of financial assets and servicing rights - Additional Information (Detail) (USD $)				3 Months Ended				3 Months Ended	12 Months Ended	3 Months Ended					3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Mar. 31, 2014 Mortgage Banking Activities [Member]	Mar. 31, 2013 Mortgage Banking Activities [Member]	Mar. 31, 2014 Loans With Recourse [Member]	Dec. 31, 2013 Loans With Recourse [Member]	Mar. 31, 2014 Buy Back Option Program [Member]	Dec. 31, 2013 Buy Back Option Program [Member]	Mar. 31, 2014 Residential Mortgage	Mar. 31, 2013 Residential Mortgage	Mar. 31, 2014 Serviced Mortgage Loans [Member]	Mar. 31, 2013 Serviced Mortgage Loans [Member]	Dec. 31, 2013 Serviced Mortgage Loans [Member]	Mar. 31, 2014 Serviced Mortgage Loans [Member] Loans With Recourse [Member]	Mar. 31, 2013 Serviced Mortgage Loans [Member] Loans With Recourse [Member]
Securitization or Asset-backed Financing Arrangement, Financial Asset for which Transfer is Accounted as Sale [Line Items]
Servicing rights on whole loan sales, principal balance												$ 32,000,000	$ 36,000,000
Securitization Financial Asset For Which Transfer Is Accounted As Sale Gain Loss On Sale										7,800,000	17,700,000	1,100,000	1,500,000
Loans serviced						2,400,000,000	2,500,000,000					16,200,000,000		16,300,000,000
Mortgage Servicing Fees Excluding Fair Value				10,751,000	11,246,000
Weighted average mortgage servicing fees	0.26%		0.27%
Mortgage loans related to buy-back option program	21,703,050,000	21,704,010,000						38,000,000	48,000,000
Repurchased Loans								$ 49,000,000	$ 209,000,000						$ 27,000,000	$ 30,000,000