Acquisitions - Summary of Merger-Related Expenses (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary of merger-related expenses
Salaries and employee benefits	$ 1,314,540	$ 1,203,993	$ 999,709
Equipment and net occupancy	257,551	249,514	216,064
Printing, postage and supplies	41,929	40,917	33,847
Other costs of operations	733,499	821,797	527,790
Total merger-related expenses		84,000
Bank Acquisition [Member]
Summary of merger-related expenses
Salaries and employee benefits	4,997	16,131	7
Equipment and net occupancy	15	412	44
Printing, postage and supplies		2,663	74
Other costs of operations	4,867	64,481	646
Total merger-related expenses	$ 9,879	$ 83,687	$ 771