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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income available to common shareholders:
Net income	$ 349,984	$ 280,401	$ 984,543	$ 808,702
Less: Preferred stock dividends	(20,318)	(20,318)	(60,953)	(60,953)
Net income available to common equity	329,666	260,083	923,590	747,749
Less: Income attributable to unvested stock-based compensation awards	(2,674)	(2,746)	(7,920)	(8,122)
Net income available to common shareholders	$ 326,992	$ 257,337	$ 915,670	$ 739,627
Weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards	156,767	134,049	158,710	133,805
Less: Unvested stock-based compensation awards	(1,274)	(1,419)	(1,374)	(1,458)
Weighted-average shares outstanding	155,493	132,630	157,336	132,347
Basic earnings per common share	$ 2.10	$ 1.94	$ 5.82	$ 5.59