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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net income available to common equity	$ 463,978	$ 507,961	$ 1,383,719	$ 1,317,471
Less: Income attributable to unvested stock-based compensation awards	(2,568)	(2,596)	(7,590)	(6,768)
Net income available to common shareholders	$ 461,410	$ 505,365	$ 1,376,129	$ 1,310,703
Adjusted weighted-average shares outstanding:
Common and unvested stock-based compensation awards	133,703	143,556	136,156	146,177
Less: Unvested stock-based compensation awards	(738)	(734)	(745)	(753)
Plus: Incremental shares from assumed conversion of stock-based compensation awards and warrants to purchase common stock	34	154	32	181
Adjusted weighted-average shares outstanding	132,999	142,976	135,443	145,605
Diluted earnings per common share	$ 3.47	$ 3.53	$ 10.16	$ 9.00