Net Income Per Common Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Net Income Per Common Share [Line Items]
Net income	$ 445,562	$ (921,813)	$ 120,817	$ 699,895	$ 1,218,504	$ (14,060)	$ (218,229)	$ 281,065	$ 344,461	$ 1,267,280	$ 1,961,471
Less: Preferred stock dividends	4,148	4,172	4,267	4,267	4,268	4,515	4,625	4,625	16,854	18,033	18,501
Net income (loss) available (related) to common shareholders	441,414	(925,985)	116,550	695,628	1,214,236	(18,575)	(222,854)	276,440	327,607	1,249,247	1,942,970
Add: Preferred Series B dividends, if dilutive										3,440	3,908
Add: Interest on Convertible Senior Note, if dilutive										21,333
Net income available to common shareholders, as adjusted									$ 327,607	$ 1,274,020	$ 1,946,878
Weighted average shares of common stock outstanding-basic	970,056,491	948,545,975	822,623,370	752,413,605	625,138,510	611,904,518	559,700,836	554,995,092	874,212,039	588,192,659	546,973,036
Add: Effect of dilutive stock options, Series B Cumulative Convertible Preferred Stock and Convertible Senior Notes, if dilutive									307,000	37,114,000	6,158,000
Weighted average shares of common stock outstanding-diluted	1,011,495,682	948,545,975	827,754,731	790,993,841	662,476,638	611,904,518	559,700,836	575,859,564	874,518,938	625,307,174	553,130,643