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, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income available to common shareholders:
Net income	$ 280,401	$ 275,344	$ 808,702	$ 788,697
Less: Preferred stock dividends	(20,318)	(20,443)	(60,953)	(55,560)
Net income available to common equity	260,083	254,901	747,749	733,137
Less: Income attributable to unvested stock-based compensation awards	(2,746)	(2,996)	(8,122)	(8,830)
Net income available to common shareholders	$ 257,337	$ 251,905	$ 739,627	$ 724,307
Weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards	134,049	132,832	133,805	132,372
Less: Unvested stock-based compensation awards	(1,419)	(1,567)	(1,458)	(1,590)
Weighted-average shares outstanding	132,630	131,265	132,347	130,782
Basic earnings per common share	$ 1.94	$ 1.92	$ 5.59	$ 5.54