Net Income Per Common Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net Income Per Common Share:
Net income	$ 700,495	$ 224,758	$ (91,159)	$ 901,806	$ 445,562	$ (921,813)	$ 120,817	$ 699,895	$ 1,735,900	$ 344,461	$ 1,267,280
Less: Preferred stock dividends	19,717	9,367	6,508	3,938	4,148	4,172	4,267	4,267	39,530	16,854	18,033
Net income (loss) available to common shareholders, prior to adjustment for dilutive potential common shares, if necessary	680,778	215,391	(97,667)	897,868	441,414	(925,985)	116,550	695,628	1,696,370	327,607	1,249,247
Add: Preferred Series B dividends, if dilutive											3,440
Add: Interest on Convertible Senior Notes, if dilutive									27,843		21,333
Net income available to common shareholders, as adjusted									$ 1,724,213	$ 327,607	$ 1,274,020
Weighted average shares of common stock outstanding-basic									972,902,459	874,212,039	588,192,659
Add: Effect of dilutive stock options, Series B Preferred Stock and Convertible Senior Notes, if dilutive									32,853,000	307,000	37,114,000
Weighted average shares of common stock outstanding-diluted									1,005,755,057	874,518,938	625,307,174