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, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net income available to common equity	$ 1,845,559	$ 1,335,572	$ 1,233,844
Less: Income attributable to unvested stock-based compensation awards	(9,524)	(8,055)	(10,363)
Net income available to common shareholders	$ 1,836,035	$ 1,327,517	$ 1,223,481
Adjusted weighted-average shares outstanding:
Common and unvested stock-based compensation awards	144,740	153,092	158,121
Less: Unvested stock-based compensation awards	(748)	(933)	(1,341)
Plus: Incremental shares from assumed conversion of stock-based compensation awards and warrants to purchase common stock	159	392	524
Adjusted weighted-average shares outstanding	144,151	152,551	157,304
Diluted earnings per common share	$ 12.74	$ 8.70	$ 7.78