Securities Available for Sale - Additional Information (Detail) (USD $)	3 Months Ended	6 Months Ended
Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	4		4
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	$ 2,000,000	$ 1,000,000	$ 4,000,000	$ 2,000,000
Fair value of pledged securities available for sale	7,600,000,000		7,600,000,000		9,100,000,000
Securities AFS Pledged Transferee Cannot Transfer	0		0		0
Securities Sold under Agreements to Repurchase	1,583,000,000		1,583,000,000		1,644,000,000
Trading Assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Trading assets and cash equivalents, pledged	978,000,000		978,000,000		770,000,000
Securities Sold under Agreements to Repurchase	930,000,000		930,000,000		747,000,000
Mortgage-backed Securities, Issued by Private Enterprises [Member] \| Other Than Temporarily Impaired Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale securities, fair market value	$ 140,000,000	$ 193,000,000	$ 140,000,000	$ 193,000,000

Disclosure regarding factors used to determine that the impairment of securities not categorized as either held-to-maturity securities or trading securities (hence equal to available for sale securities) where cost exceeds fair value is not an other than temporary impairment (OTTI). This item contains disclosure of the number of investment positions in the available-for-sale investments determined to be temporarily impaired.

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The amount of other than temporary impairment losses on investments in debt and equity securities categorized as Available-for-sale which have been recognized in earnings during the period. Such impairment losses consist of other than temporary impairments (OTTI) on equity securities, credit losses on investments in debt securities, and when the entity intends to sell an impaired debt security or it is more likely than not that the entity will be required to sell the impaired debt security before recovery of its amortized cost basis.

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- Definition

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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