Results of Operations and Average Assets by Segment (Parenthetical) (Detail) (USD $) In Millions	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Segment Reporting Information [Line Items]
Fully taxable-equivalent adjustments	$ 5	$ 5	$ 9	$ 9

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