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, 2018	Dec. 31, 2017	Dec. 31, 2016
Income available to common shareholders:
Net income	$ 1,918,080	$ 1,408,306	$ 1,315,114
Less: Preferred stock dividends	(72,521)	(72,734)	(81,270)
Net income available to common equity	1,845,559	1,335,572	1,233,844
Less: Income attributable to unvested stock-based compensation awards	(9,531)	(8,069)	(10,385)
Net income available to common shareholders	$ 1,836,028	$ 1,327,503	$ 1,223,459
Weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards	144,740	153,092	158,121
Less: Unvested stock-based compensation awards	(748)	(933)	(1,341)
Weighted-average shares outstanding	143,992	152,159	156,780
Basic earnings per common share	$ 12.75	$ 8.72	$ 7.80