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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income available to common shareholders:
Net income	$ 473,260	$ 493,160	$ 956,002	$ 845,770
Less: Preferred stock dividends	(18,130)	(18,130)	(36,260)	(36,260)
Net income available to common equity	455,130	475,030	919,742	809,510
Less: Income attributable to unvested stock-based compensation awards	(2,498)	(2,432)	(5,024)	(4,172)
Net income available to common shareholders	$ 452,632	$ 472,598	$ 914,718	$ 805,338
Weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards	136,182	145,571	137,403	147,510
Less: Unvested stock-based compensation awards	(749)	(746)	(749)	(764)
Weighted-average shares outstanding	135,433	144,825	136,654	146,746
Basic earnings per common share	$ 3.34	$ 3.26	$ 6.69	$ 5.49