Initial fair value of assets obtained as proceeds from residential mortgage loans securitized (Detail) (Residential Mortgage, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	$ 231,713	$ 418,137
Trading Account Assets[Member]
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	228,515	413,394
Trading Account Assets[Member] | Government National Mortgage Association Certificates And Obligations GNMA Member
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	165,932	285,252
Trading Account Assets[Member] | Federal National Mortgage Association Certificates And Obligations FNMA Member
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	62,583	128,142
Trading Account Assets[Member] | Federal Home Loan Mortgage Corporation Certificates And Obligations FHLMC Member
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	0	0
Servicing Asset At Fair Value Amount [Member]
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	3,198	4,743
Fair Value, Inputs, Level 1 [Member]
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	0	0
Fair Value, Inputs, Level 1 [Member] | Trading Account Assets[Member]
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	0	0
Fair Value, Inputs, Level 1 [Member] | Trading Account Assets[Member] | Government National Mortgage Association Certificates And Obligations GNMA Member
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	0	0
Fair Value, Inputs, Level 1 [Member] | Trading Account Assets[Member] | Federal National Mortgage Association Certificates And Obligations FNMA Member
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	0	0
Fair Value, Inputs, Level 1 [Member] | Trading Account Assets[Member] | Federal Home Loan Mortgage Corporation Certificates And Obligations FHLMC Member
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	0	0
Fair Value, Inputs, Level 1 [Member] | Servicing Asset At Fair Value Amount [Member]
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	0	0
Fair Value, Inputs, Level 2 [Member]
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	228,515	413,394
Fair Value, Inputs, Level 2 [Member] | Trading Account Assets[Member]
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	228,515	413,394
Fair Value, Inputs, Level 2 [Member] | Trading Account Assets[Member] | Government National Mortgage Association Certificates And Obligations GNMA Member
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	165,932	285,252
Fair Value, Inputs, Level 2 [Member] | Trading Account Assets[Member] | Federal National Mortgage Association Certificates And Obligations FNMA Member
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	62,583	128,142
Fair Value, Inputs, Level 2 [Member] | Trading Account Assets[Member] | Federal Home Loan Mortgage Corporation Certificates And Obligations FHLMC Member
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	0	0
Fair Value, Inputs, Level 2 [Member] | Servicing Asset At Fair Value Amount [Member]
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	0	0
Fair Value, Inputs, Level 3 [Member]
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	3,198	4,743
Fair Value, Inputs, Level 3 [Member] | Trading Account Assets[Member]
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	0	0
Fair Value, Inputs, Level 3 [Member] | Trading Account Assets[Member] | Government National Mortgage Association Certificates And Obligations GNMA Member
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	0	0
Fair Value, Inputs, Level 3 [Member] | Trading Account Assets[Member] | Federal National Mortgage Association Certificates And Obligations FNMA Member
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	0	0
Fair Value, Inputs, Level 3 [Member] | Trading Account Assets[Member] | Federal Home Loan Mortgage Corporation Certificates And Obligations FHLMC Member
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	0	0
Fair Value, Inputs, Level 3 [Member] | Servicing Asset At Fair Value Amount [Member]
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	$ 3,198	$ 4,743