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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income available to common shareholders:
Net income	$ 526,091	$ 355,923	$ 1,371,861	$ 1,085,903
Less: Preferred stock dividends	(18,130)	(18,130)	(54,390)	(54,604)
Net income available to common equity	507,961	337,793	1,317,471	1,031,299
Less: Income attributable to unvested stock-based compensation awards	(2,598)	(1,992)	(6,774)	(6,288)
Net income available to common shareholders	$ 505,363	$ 335,801	$ 1,310,697	$ 1,025,011
Weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards	143,556	152,245	146,177	153,814
Less: Unvested stock-based compensation awards	(734)	(898)	(753)	(948)
Weighted-average shares outstanding	142,822	151,347	145,424	152,866
Basic earnings per common share	$ 3.54	$ 2.22	$ 9.01	$ 6.71