Detailed Analysis of Contractual Maturities and Next Call Dates of Outstanding Repurchase Agreements (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Amount
Contractual Maturity Over 90 days, amount	$ 4,125,000	$ 4,125,000
Weighted Average Interest Rate
Contractual Maturity Over 90 days, Weighted Average Interest Rate	3.54%
Contractual Maturity
Amount
2013	700,000
2015	100,000
2016	345,000
2017	1,080,000
2018	1,600,000
2020	300,000
Contractual Maturity Over 90 days, amount	4,125,000
Weighted Average Interest Rate
2013	3.04%
2015	2.50%
2016	4.09%
2017	4.08%
2018	3.48%
2020	2.93%
Contractual Maturity Over 90 days, Weighted Average Interest Rate	3.54%
Earlier of Contractual Maturity or Next Call Date
Amount
2012	3,643,000
2013	200,000
2015	100,000
2016	182,000
Contractual Maturity Over 90 days, amount	$ 4,125,000
Weighted Average Interest Rate
2012	3.61%
2013	2.83%
2015	2.50%
2016	3.58%
Contractual Maturity Over 90 days, Weighted Average Interest Rate	3.54%

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Amount of cash received as security in return for loaning securities to another party which are due from five to six years of the Balance Sheet date.

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Amount of cash received as security in return for loaning securities to another party which are due from four to five years of the Balance Sheet date.

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Securities Sold under Agreements to Repurchase, Maturities Summary, Due from Nine to Ten Years of Balance Sheet Date

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Amount of cash received as security in return for loaning securities to another party which are due from one to two years of the Balance Sheet date.

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Amount of cash received as security in return for loaning securities to another party which are due from seven to eight years of the Balance Sheet date.

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Amount of cash received as security in return for loaning securities to another party which are due from six to seven years of the Balance Sheet date.

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Amount of cash received as security in return for loaning securities to another party which are due within one year of the Balance Sheet date.

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The weighted average interest rate applicable to the cash received as security in return for loaning securities to another party which are due from five to six years of the Balance Sheet date.

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No definition available.

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The weighted average interest rate applicable to the cash received as security in return for loaning securities to another party which are due from four to five years of the Balance Sheet date.

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No definition available.

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Securities Sold under Agreements to Repurchase, Maturities Summary, Weighted Average Interest Rate, Nine to Ten Years from Balance Sheet Date

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The weighted average interest rate applicable to the cash received as security in return for loaning securities to another party which are due within one year of the Balance Sheet date.

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The weighted average interest rate applicable to the cash received as security in return for loaning securities to another party which are due from one to two years of the Balance Sheet date.

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The weighted average interest rate applicable to the cash received as security in return for loaning securities to another party which are due from seven to eight years of the Balance Sheet date.

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No definition available.

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The weighted average interest rate applicable to the cash received as security in return for loaning securities to another party which are due from six to seven years of the Balance Sheet date.

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The interest rate associated with the repurchase agreements. This is also known as the repo rate.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 4

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The carrying value as of the balance sheet date of securities that an institution sells and agrees to repurchase (the identical or substantially the same securities) as a seller-borrower at a specified date for a specified price, also known as a repurchase agreement, or repo. Most repos involve obligations of the federal government or its agencies, but other financial instruments, such as commercial paper, banker's acceptances, and negotiable certificates of deposit, are sometimes used in repos.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

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-Name Audit and Accounting Guide (AAG)

-Number AAG-BRD

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