Earnings Per Common Share - Computations of Basic Earnings Per Common Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income available to common shareholders:
Net income	$ 1,066,246	$ 1,138,480	$ 1,029,498
Less: Preferred stock dividends	(75,878)	(54,120)	(53,450)
Amortization of preferred stock discount		(7,942)	(8,026)
Net income available to common equity	990,368	1,076,418	968,022
Less: Income attributable to unvested stock-based compensation awards	(11,837)	(13,989)	(14,632)
Net income available to common shareholders	$ 978,531	$ 1,062,429	$ 953,390
Weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards	132,532	130,354	127,793
Less: Unvested stock-based compensation awards	(1,582)	(1,700)	(1,929)
Weighted-average shares outstanding	130,950	128,654	125,864
Basic earnings per common share	$ 7.47	$ 8.26	$ 7.57