Earnings Per Common Share - Computations of Diluted Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Net income available to common equity	$ 260,083	$ 254,901	$ 747,749	$ 733,137
Less: Income attributable to unvested stock-based compensation awards	(2,737)	(2,984)	(8,093)	(8,793)
Net income available to common shareholders	$ 257,346	$ 251,917	$ 739,656	$ 724,344
Adjusted weighted-average shares outstanding:
Common and unvested stock-based compensation awards	134,049	132,832	133,805	132,372
Less: Unvested stock-based compensation awards	(1,419)	(1,567)	(1,458)	(1,590)
Plus: Incremental shares from assumed conversion of stock-based compensation awards and warrants to purchase common stock	746	863	742	916
Adjusted weighted-average shares outstanding	133,376	132,128	133,089	131,698
Diluted earnings per common share	$ 1.93	$ 1.91	$ 5.56	$ 5.50