Earnings Per Common Share - Computations of Basic Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income available to common shareholders:
Net income	$ 458,069	$ 241,054	$ 905,318	$ 509,876
Less: Preferred stock dividends	(17,050)	(17,050)	(34,100)	(34,128)
Net income available to common equity	441,019	224,004	871,218	475,748
Less: Income attributable to unvested stock-based compensation awards	(2,263)	(906)	(4,370)	(1,954)
Net income available to common shareholders	$ 438,756	$ 223,098	$ 866,848	$ 473,794
Weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards	129,589	129,059	129,502	129,750
Less: Unvested stock-based compensation awards	(918)	(784)	(898)	(764)
Weighted-average shares outstanding	128,671	128,275	128,604	128,986
Basic earnings per common share	$ 3.41	$ 1.74	$ 6.74	$ 3.67