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, 2016	Dec. 31, 2015	Dec. 31, 2014
Income available to common shareholders:
Net income	$ 1,315,114	$ 1,079,667	$ 1,066,246
Less: Preferred stock dividends	(81,270)	(81,270)	(75,878)
Net income available to common equity	1,233,844	998,397	990,368
Less: Income attributable to unvested stock-based compensation awards	(10,385)	(10,708)	(11,837)
Net income available to common shareholders	$ 1,223,459	$ 987,689	$ 978,531
Weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards	158,121	138,285	132,532
Less: Unvested stock-based compensation awards	(1,341)	(1,482)	(1,582)
Weighted-average shares outstanding	156,780	136,803	130,950
Basic earnings per common share	$ 7.80	$ 7.22	$ 7.47