CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash flows from operating activities:
Net income (loss)	$ 1,735,900,000	$ 344,461,000	$ 1,267,280,000
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Amortization of Investment premiums and discounts, net	1,470,801,000	794,205,000	664,429,000
Amortization of intangibles	4,080,000	2,300,000	1,600,000
Amortization of deferred expenses	6,965,000	3,600,000	3,150,000
Amortization of contingent beneficial conversion feature and equity component on Convertible Senior Notes	18,017,000	7,550,000
(Gains) losses on disposal of investments	(432,139,000)	(206,846,000)	(181,791,000)
Net loss on extinguishment of 4% Convertible Senior Notes	162,340,000
Stock option and long-term compensation expense	5,584,000	5,269,000	4,757,000
Non-cash component of disposal of subsidiary	(1,177,000)
Unrealized (gains) losses on interest rate swaps	32,219,000	1,815,107,000	318,832,000
Net unrealized (gains) losses on interest-only Agency mortgage-backed securities	59,937,000	106,657,000
Net (gains) losses on trading assets	(20,525,000)	(21,398,000)	2,351,000
(Gain) loss on investment with affiliate, equity method		(98,000)	(318,000)
Unrealized (gains) losses on equity securities		100,000
Proceeds from repurchase agreements from RCap	733,739,097,000	877,734,065,000	1,268,429,168,000
Payments on repurchase agreements from RCap	(727,275,192,000)	(878,806,056,000)	(1,258,941,064,000)
Proceeds from reverse repurchase agreements to RCap	401,926,011,000	156,659,365,000	87,968,002,000
Payments on reverse repurchase agreements to RCap	(402,805,044,000)	(156,502,577,000)	(88,479,412,000)
Proceeds from reverse repurchase agreements to Shannon	680,525,000	166,354,000
Payments on reverse repurchase agreements to Shannon	(751,721,000)	(177,845,000)
Proceeds from securities borrowed	74,361,498,000	27,261,366,000	2,924,082,000
Payments on securities borrowed	(75,593,708,000)	(27,973,422,000)	(3,111,681,000)
Proceeds from securities loaned	185,657,591,000	54,126,121,000	3,231,198,000
Payments on securities loaned	(184,654,177,000)	(53,539,061,000)	(3,042,414,000)
Proceeds from U.S. Treasury Securities	64,028,348,000	29,168,074,000	9,331,089,000
Payments on U.S. Treasury Securities	(64,746,420,000)	(28,490,573,000)	(9,521,134,000)
Net payments on derivatives	(10,173,000)	(7,158,000)	(3,455,000)
Net change in:
Other assets	(9,243,000)	(3,258,000)	3,950,000
Accrued interest and dividends receivable	(6,151,000)	(64,362,000)	(27,125,000)
Advisory and service fees receivable	1,820,000	(3,378,000)	(3,606,000)
Receivable from Prime Broker	3,272,000
Accrued interest payable	47,931,000	23,199,000	26,306,000
Accounts payable and other liabilities	3,241,000	(1,698,000)	(1,084,000)
Net cash provided by (used in) operating activities	7,639,507,000	2,420,063,000	10,863,110,000
Cash flows from investing activities:
Payments on purchases of Agency mortgage-backed securities and debentures	(86,161,777,000)	(69,065,069,000)	(54,424,951,000)
Proceeds from sales of Agency mortgage-backed securities and debentures	30,542,875,000	19,337,053,000	9,262,772,000
Principal payments on Agency mortgage-backed securities	35,133,544,000	23,565,709,000	28,961,203,000
Proceeds from Agency debentures called	1,801,283,000	1,124,000,000	2,132,002,000
Payments on purchase of corporate debt	(81,090,000)	(31,675,000)	(21,670,000)
Proceeds from corporate debt called	67,649,000
Principal payments on corporate debt	4,247,000	1,375,000
Net gains (losses) on other derivative securities	10,379,000	13,965,000
Earn out payment	(13,387,000)		(14,113,000)
Purchase of investment in affiliate		(57,500,000)
Purchase of customer relationships		(3,555,000)
Purchase of equity securities		(3,990,000)
Proceeds from sales of equity securities	4,048,000
Proceeds from reverse repurchase agreements			4,291,430,000
Payments on reverse repurchase agreements			(4,032,426,000)
Payment on disposal of subsidiary	(800,000)
Net cash provided by (used in) investing activities	(18,693,029,000)	(25,119,687,000)	(13,845,753,000)
Cash flows from financing activities:
Proceeds from repurchase agreements	352,497,651,000	273,023,622,000	224,789,731,000
Principal payments on repurchase agreements	(340,273,744,000)	(253,387,283,000)	(223,342,427,000)
Proceeds from exercise of stock options	8,438,000	8,953,000	4,598,000
Net payment on extinguishment of 4% Convertible Senior Notes	(617,476,000)
Net proceeds from direct purchases and dividend reinvestments	2,794,000	455,547,000	278,784,000
Net proceeds from common stock follow-on offerings	(248,000)	5,351,846,000	1,047,354,000
Net payment on share repurchase	(255,901,000)
Dividends paid	(2,149,872,000)	(2,041,489,000)	(1,599,339,000)
Net cash provided by (used in) financing activities	10,675,113,000	23,411,196,000	1,760,701,000
Net increase (decrease) in cash and cash equivalents	(378,409,000)	711,572,000	(1,221,942,000)
Cash and cash equivalents, beginning of period	994,198,000	282,626,000	1,504,568,000
Cash and cash equivalents, end of period	615,789,000	994,198,000	282,626,000
Supplemental disclosure of cash flow information:
Interest received	4,718,524,000	4,309,690,000	3,322,228,000
Dividends received	29,522,000	31,876,000	30,042,000
Fees received	84,483,000	75,827,000	54,467,000
Interest paid (excluding interest paid on interest rate swaps)	595,152,000	455,873,000	411,608,000
Net interest paid on interest rate swaps	892,656,000	876,099,000	725,418,000
Taxes paid	52,590,000	61,045,000	36,742,000
Noncash investing activities:
Receivable for Investments sold	290,722,000		151,460,000
Payable for Investments purchased	8,256,957,000	4,315,796,000	4,575,026,000
Net change in unrealized gains (losses) on available-for-sale securities and interest rate swaps, net of reclassification adjustment	44,254,000	1,844,346,000	(726,675,000)
Noncash financing activities:
Dividends declared, not yet paid	432,154,000	552,806,000	404,220,000
Conversion of Series B Cumulative Convertible preferred stock	32,272,000	7,759,000	23,081,000
Contingent beneficial conversion feature on 4% Convertible Senior Notes	61,725,000	60,087,000
Equity component of 5% Convertible Senior Notes	11,717,000
7.625% Series C Cumulative Redeemable Preferred Stock [Member]
Cash flows from financing activities:
Net proceeds from preferred stock offering	290,514,000
7.50% Series D Cumulative Redeemable Preferred Stock [Member]
Cash flows from financing activities:
Net proceeds from preferred stock offering	445,457,000
Convertible Senior Notes 5.00 Percent Due 2015 [Member]
Cash flows from financing activities:
Net proceeds from issuance of convertible Senior Notes	727,500,000
Convertible Senior Notes 4.00 Percent Due 2015 [Member]
Cash flows from financing activities:
Net proceeds from issuance of convertible Senior Notes			$ 582,000,000