Securities - Additional Information (Detail) (USD $)	3 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Investments Debt And Equity Securities [Abstract]
Available for sale securities reclassified to held to maturity securities	$ 1,000,000,000
Unrealized net holding gain on the available for sale securities on the date of transfer	56,800,000
Gains or losses recognized as a result of transfer	0
Securities pledged to secure public deposits and securities sold under agreements to repurchase	$ 2,600,000,000	$ 2,600,000,000