Earnings Per Common Share - Computations of Diluted Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Net income available to common equity	$ 1,284,924	$ 1,859,708	$ 1,845,559
Less: Income attributable to unvested stock-based compensation awards	(5,856)	(10,197)	(9,524)
Net income available to common shareholders	$ 1,279,068	$ 1,849,511	$ 1,836,035
Adjusted weighted-average shares outstanding:
Common and unvested stock-based compensation awards	129,404	135,169	144,740
Less: Unvested stock-based compensation awards	(766)	(741)	(748)
Plus: Incremental shares from assumed conversion of stock-based compensation awards and warrants to purchase common stock	66	34	159
Adjusted weighted-average shares outstanding	128,704	134,462	144,151
Diluted earnings per common share	$ 9.94	$ 13.75	$ 12.74