Earnings Per Common Share - Computations of Basic 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
Income available to common shareholders:
Net income	$ 372,136	$ 480,081	$ 882,012	$ 1,436,083
Less: Preferred stock dividends	(17,050)	(16,103)	(51,178)	(52,364)
Net income available to common equity	355,086	463,978	830,834	1,383,719
Less: Income attributable to unvested stock-based compensation awards	(1,687)	(2,568)	(3,631)	(7,591)
Net income available to common shareholders	$ 353,399	$ 461,410	$ 827,203	$ 1,376,128
Weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards	129,061	133,703	129,518	136,156
Less: Unvested stock-based compensation awards	(776)	(738)	(768)	(745)
Weighted-average shares outstanding	128,285	132,965	128,750	135,411
Basic earnings per common share	$ 2.75	$ 3.47	$ 6.42	$ 10.16