Securities Financing Activities - Summarized Securities Financing Agreements (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	$ 6	$ 4	$ 4
Total offsetting of financial assets	6	4	4
Gross Amount Presented in Balance Sheet [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	334	271	338
Securities borrowed	1		5
Total offsetting of financial assets	335	271	343
Repurchase agreements	350	228	481
Total offsetting of financial liabilities	350	228	481
Netting Adjustments [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	(93)	(95)	(272)
Total offsetting of financial assets	(93)	(95)	(272)
Repurchase agreements	(93)	(95)	(272)
Total offsetting of financial liabilities	(93)	(95)	(272)
Collateral [Member]
Securities Financing Transaction [Line Items]
Reverse repurchase agreements	(235)	(172)	(62)
Securities borrowed	(1)		(5)
Total offsetting of financial assets	(236)	(172)	(67)
Repurchase agreements	(257)	(133)	(209)
Total offsetting of financial liabilities	$ (257)	$ (133)	$ (209)

The carrying value as of the balance sheet date of securities borrowed from broker-dealers or institutions (a) to deliver them in place of securities not available because of short-sales or late or ineffective deliveries; (b) to lend them in connection with finder or conduit transactions; and (c) to be used for other purposes permitted under federal regulations.

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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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