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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net income available to common equity	$ 355,086	$ 463,978	$ 830,834	$ 1,383,719
Less: Income attributable to unvested stock-based compensation awards	(1,686)	(2,568)	(3,630)	(7,590)
Net income available to common shareholders	$ 353,400	$ 461,410	$ 827,204	$ 1,376,129
Adjusted weighted-average shares outstanding:
Common and unvested stock-based compensation awards	129,061	133,703	129,518	136,156
Less: Unvested stock-based compensation awards	(776)	(738)	(768)	(745)
Plus: Incremental shares from assumed conversion of stock-based compensation awards and warrants to purchase common stock	70	34	63	32
Adjusted weighted-average shares outstanding	128,355	132,999	128,813	135,443
Diluted earnings per common share	$ 2.75	$ 3.47	$ 6.42	$ 10.16