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, 2015	Dec. 31, 2014	Dec. 31, 2013
Income available to common shareholders:
Net income	$ 1,079,667	$ 1,066,246	$ 1,138,480
Less: Preferred stock dividends	(81,270)	(75,878)	(54,120)
Amortization of preferred stock discount			(7,942)
Net income available to common equity	998,397	990,368	1,076,418
Less: Income attributable to unvested stock-based compensation awards	(10,708)	(11,837)	(13,989)
Net income available to common shareholders	$ 987,689	$ 978,531	$ 1,062,429
Weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards	138,285	132,532	130,354
Less: Unvested stock-based compensation awards	(1,482)	(1,582)	(1,700)
Weighted-average shares outstanding	136,803	130,950	128,654
Basic earnings per common share	$ 7.22	$ 7.47	$ 8.26