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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income available to common shareholders:
Net income	$ 381,053	$ 336,031	$ 729,980	$ 634,559
Less: Preferred stock dividends	(18,237)	(20,317)	(36,474)	(40,635)
Net income available to common equity	362,816	315,714	693,506	593,924
Less: Income attributable to unvested stock-based compensation awards	(2,158)	(2,746)	(4,298)	(5,227)
Net income available to common shareholders	$ 360,658	$ 312,968	$ 689,208	$ 588,697
Weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards	153,770	159,164	154,612	159,692
Less: Unvested stock-based compensation awards	(913)	(1,362)	(974)	(1,424)
Weighted-average shares outstanding	152,857	157,802	153,638	158,268
Basic earnings per common share	$ 2.36	$ 1.98	$ 4.49	$ 3.72