Commitments and Contingencies - Company's Significant Commitments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Commitments to extend credit
Home equity lines of credit	$ 6,239,383	$ 6,282,615
Commercial real estate loans to be sold	60,479	139,929
Other commercial real estate and construction	3,877,466	3,819,342
Residential real estate loans to be sold	647,523	1,550,441
Other residential real estate	410,647	445,268
Commercial and other	10,629,010	10,070,711
Standby letters of credit	3,684,608	4,025,329
Commercial letters of credit	49,757	53,201
Financial guarantees, indemnification contracts and other	2,394,180	2,120,361
Commitments to sell real estate loans	$ 1,294,488	$ 2,625,408