Earnings Per Common Share - Computations of Basic Earnings Per Common Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income available to common shareholders:
Net income	$ 294,479	$ 293,462	$ 917,058	$ 733,305
Less: Preferred stock dividends	(13,363)	(13,363)	(40,088)	(40,088)
Amortization of preferred stock discount	(2,235)	(2,033)	(6,575)	(5,921)
Net income available to common equity	278,881	278,066	870,395	687,296
Less: Income attributable to unvested stock-based compensation awards	(3,545)	(4,181)	(11,451)	(10,475)
Net income available to common shareholders	$ 275,336	$ 273,885	$ 858,944	$ 676,821
Weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards	130,836	127,741	130,088	127,449
Less: Unvested stock-based compensation awards	(1,665)	(1,923)	(1,719)	(1,939)
Weighted-average shares outstanding	129,171	125,818	128,369	125,510
Basic earnings per common share	$ 2.13	$ 2.18	$ 6.69	$ 5.39