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, 2012	Mar. 31, 2011
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	$ 252,946	$ 334,541
Trading Account Assets[Member]
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	249,713	328,592
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	190,178	255,574
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	59,535	73,018
Servicing Asset At Fair Value Amount [Member]
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	3,233	5,949
Availableforsale Securities Member
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	0	0
Availableforsale Securities 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
Availableforsale Securities 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]
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] | 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 1 [Member] | Availableforsale Securities 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] | Availableforsale Securities 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] | Availableforsale Securities 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 2 [Member]
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	249,713	328,592
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	249,713	328,592
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	190,178	255,574
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	59,535	73,018
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 2 [Member] | Availableforsale Securities 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] | Availableforsale Securities 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 2 [Member] | Availableforsale Securities 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]
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	3,233	5,949
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] | Servicing Asset At Fair Value Amount [Member]
Assets
Transfers Of Financial Assets Accounted For As Sale Initial Fair Value Of Asset Obtained As Proceeds	3,233	5,949
Fair Value, Inputs, Level 3 [Member] | Availableforsale Securities 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] | Availableforsale Securities 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] | Availableforsale Securities 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