Earnings Per Common Share - Computations of Diluted Earnings Per Common Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Earnings Per Share [Abstract]
Net income available to common equity	$ 214,343	$ 258,603
Less: Income attributable to unvested stock-based compensation awards	(2,612)	(3,507)
Net income available to common shareholders	$ 211,731	$ 255,096
Adjusted weighted-average shares outstanding:
Common and unvested stock-based compensation awards	131,800	129,449
Less: Unvested stock-based compensation awards	(1,588)	(1,780)
Plus: Incremental shares from assumed conversion of stock-based compensation awards	914	967
Adjusted weighted-average shares outstanding	131,126	128,636
Diluted earnings per common share	$ 1.61	$ 1.98