Earnings Per Common Share - Computations of Diluted 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
Earnings Per Share [Abstract]
Net income available to common equity	$ 998,397	$ 990,368	$ 1,076,418
Less: Income attributable to unvested stock-based compensation awards	(10,673)	(11,787)	(13,922)
Net income available to common shareholders	$ 987,724	$ 978,581	$ 1,062,496
Adjusted weighted-average shares outstanding:
Common and unvested stock-based compensation awards	138,285	132,532	130,354
Less: Unvested stock-based compensation awards	(1,482)	(1,582)	(1,700)
Plus: Incremental shares from assumed conversion of stock-based compensation awards and warrants to purchase common stock	730	894	949
Adjusted weighted-average shares outstanding	137,533	131,844	129,603
Diluted earnings per common share	$ 7.18	$ 7.42	$ 8.20