Earnings Per Common Share - Computations of Diluted Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share [Abstract]
Net income available to common equity	$ 362,816	$ 315,714	$ 693,506	$ 593,924
Less: Income attributable to unvested stock-based compensation awards	(2,154)	(2,740)	(4,289)	(5,217)
Net income available to common shareholders	$ 360,662	$ 312,974	$ 689,217	$ 588,707
Adjusted weighted-average shares outstanding:
Common and unvested stock-based compensation awards	153,770	159,164	154,612	159,692
Less: Unvested stock-based compensation awards	(913)	(1,362)	(974)	(1,424)
Plus: Incremental shares from assumed conversion of stock-based compensation awards and warrants to purchase common stock	419	539	470	493
Adjusted weighted-average shares outstanding	153,276	158,341	154,108	158,761
Diluted earnings per common share	$ 2.35	$ 1.98	$ 4.47	$ 3.71