Commitments and Contingencies - Company's Significant Commitments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Commitments to extend credit
Home equity lines of credit	$ 6,260,931	$ 6,218,823
Commercial real estate loans to be sold	151,989	62,386
Other commercial real estate and construction	4,055,951	3,919,545
Residential real estate loans to be sold	521,869	469,869
Other residential real estate	368,055	384,617
Commercial and other	10,781,231	10,419,545
Standby letters of credit	3,531,586	3,600,528
Commercial letters of credit	39,197	53,284
Financial guarantees and indemnification contracts	2,842,506	2,457,633
Commitments to sell real estate loans	$ 845,549	$ 854,656