Deposits - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Deposits [Abstract]
Time deposit accounts individually equal to or greater than $100,000	$ 133	$ 126
Interest expense paid on time deposit accounts individually equal to or greater than $100,000	0.5	0.9	1.5
Time deposit accounts individually equal to or greater than $100,000 scheduled to mature within one year	$ 133