Earnings Per Common Share - Computations of Basic 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
Income available to common shareholders:
Net income	$ 1,353,152	$ 1,929,149	$ 1,918,080
Less: Preferred stock dividends	(68,228)	(69,441)	(72,521)
Net income available to common equity	1,284,924	1,859,708	1,845,559
Less: Income attributable to unvested stock-based compensation awards	(5,858)	(10,199)	(9,531)
Net income available to common shareholders	$ 1,279,066	$ 1,849,509	$ 1,836,028
Weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards	129,404	135,169	144,740
Less: Unvested stock-based compensation awards	(766)	(741)	(748)
Weighted-average shares outstanding	128,638	134,428	143,992
Basic earnings per common share	$ 9.94	$ 13.76	$ 12.75