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		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Income available to common shareholders:
Net income	$ 348,466	$ 233,380	$ 622,579	$ 439,843
Less: Preferred stock dividends	(13,362)	(13,362)	(26,725)	(26,725)
Amortization of preferred stock discount	(2,193)	(1,964)	(4,340)	(3,888)
Net income available to common equity	332,911	218,054	591,514	409,230
Less: Income attributable to unvested stock-based compensation awards	(4,373)	(3,345)	(7,917)	(6,283)
Net income available to common shareholders	$ 328,538	$ 214,709	$ 583,597	$ 402,947
Weighted-average shares outstanding:
Common shares outstanding (including common stock issuable) and unvested stock-based compensation awards	129,964	127,445	129,708	127,301
Less: Unvested stock-based compensation awards	(1,712)	(1,957)	(1,746)	(1,947)
Weighted-average shares outstanding	128,252	125,488	127,962	125,354
Basic earnings per common share	$ 2.56	$ 1.71	$ 4.56	$ 3.21