Commitments and Contingencies - Company's Significant Commitments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Commitments to extend credit
Home equity lines of credit	$ 6,276,882	$ 6,282,615
Commercial real estate loans to be sold	247,411	139,929
Other commercial real estate and construction	4,301,842	3,819,342
Residential real estate loans to be sold	895,796	1,550,441
Other residential real estate	440,030	445,268
Commercial and other	10,079,740	10,070,711
Standby letters of credit	3,848,708	4,025,329
Commercial letters of credit	36,058	53,201
Financial guarantees, indemnification contracts and other	2,600,259	2,120,361
Commitments to sell real estate loans	$ 3,016,980	$ 2,625,408