Restrictions on cash and due from banks and certain securities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011
Restricted Cash and Cash Equivalents Items [Line Items]
Average Reserve Required With Federal Reserve Bank	$ 877	$ 838	$ 843
Restricted Cash And Cash Equivalents	$ 36	$ 36	$ 51

- Definition

The carrying amounts of cash and cash equivalent items which are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. This element is for unclassified presentations; for classified presentations there is a separate and distinct element.

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