Repurchase Agreements - Narrative (Detail) (USD $)	Dec. 31, 2011 Day	Dec. 31, 2010 Day
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements - outstanding	$ 84,097,885,000	$ 65,533,537,000
Repurchase agreements - weighted average borrowing rates	1.59%	1.84%
Repurchase agreements - weighted average remaining maturities (in days)	103	127
Repurchase agreements - collateral held, fair value	91,300,000,000	69,500,000,000
Repurchase agreements - amount at risk not greater than percent	10.00%	10.00%
Over 1 year [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements - outstanding	4,900,000,000	6,400,000,000
Repurchase agreements - fair value	$ 5,200,000,000	$ 6,700,000,000

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. The amount of securities that an institution sells and agrees to repurchase (seller-borrower) at a specified date for a specified price, net of any reductions or offsets. Most repurchase agreements 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 (CDs), are sometimes used in repurchase agreements. A repurchase agreement is similar to the seller-borrower's borrowing funds equal to the sales price of the related securities with the securities as collateral. Maturities of such agreements are flexible and generally vary from one day to 270 days.

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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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