CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Statement of Cash Flows [Abstract]
Net income (loss)	$ (1,768,407)	$ (3,372,833)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities
Amortization of premiums and discounts of investments, net	1,130,285	943,277
Amortization of securitized debt premiums and discounts and deferred financing costs	(7,263)	(11,457)
Depreciation, amortization and other noncash expenses	28,181	24,107
Net (gains) losses on disposal of investments and other	(652,150)	65,727
Net (gains) losses on investments and derivatives	2,889,963	2,589,685
Income from unconsolidated joint ventures	(2,596)	3,350
Loan loss provision	146,084	9,207
Payments on purchases of loans held for sale	(120,855)	(196,252)
Proceeds from sales and repayments of loans held for sale	139,672	220,409
Net receipts (payments) on derivatives	(2,210,881)	(2,561,170)
Net change in
Other assets	291,745	(45,547)
Interest receivable	148,165	(92,959)
Interest payable	(320,997)	(5,131)
Other liabilities	(30,769)	34,194
Net cash provided by (used in) operating activities	(339,823)	(2,395,393)
Cash flows from investing activities
Payments on purchases of securities	(24,970,238)	(51,502,672)
Proceeds from sales of securities	50,295,038	19,713,184
Principal payments on securities	14,392,160	11,206,792
Payments on purchases and origination of loans	(1,658,578)	(2,718,403)
Proceeds from sales of loans	583,040	365,787
Principal payments on loans	1,558,859	2,523,471
Investments in real estate	(6,123)	(12,384)
Proceeds from sales of real estate	0
Proceeds from sales of real estate		6,661
Proceeds from reverse repurchase agreements	46,100,000	78,439,755
Payments on reverse repurchase agreements	(46,100,000)	(77,789,715)
Distributions in excess of cumulative earnings from unconsolidated joint ventures	6,641	1,975
Cash acquired in asset acquisition	1,047	0
Net cash provided by (used in) investing activities	40,201,846	(19,765,549)
Cash flows from financing activities
Proceeds from repurchase agreements and other secured financing	2,353,694,509	4,275,937,246
Payments on repurchase agreements and other secured financing	(2,394,417,060)	(4,254,088,297)
Proceeds from issuances of securitized debt	2,385,374	2,030,356
Principal payments on securitized debt	(860,306)	(1,778,314)
Payment of deferred financing cost	(553)	(5,222)
Net proceeds from stock offerings, direct purchases and dividend reinvestments	1,075	1,829,025
Redemptions of preferred stock	0	(230,000)
Net principal receipts (payments) on mortgages payable	22,550	(25,398)
Net contributions (distributions) from (to) noncontrolling interests	8,167	(987)
Net payment on share repurchase	(175,076)	(155,304)
Dividends paid	(1,131,450)	(1,293,991)
Net cash provided by (used in) financing activities	(40,472,770)	22,219,114
Net (decrease) increase in cash and cash equivalents	(610,747)	58,172
Cash and cash equivalents including cash pledged as collateral, beginning of period	1,850,729	1,735,749
Cash and cash equivalents including cash pledged as collateral, end of period	1,239,982	1,793,921
Supplemental disclosure of cash flow information
Interest received	2,926,598	3,583,189
Dividends received	4,485	6,279
Interest paid (excluding interest paid on interest rate swaps)	1,050,203	2,041,539
Net interest paid on interest rate swaps	290,277	(96,169)
Taxes received (paid)	1,551	274
Noncash investing and financing activities
Receivable for unsettled trades	54,200	193,229
Payable for unsettled trades	1,176,001	245,626
Net change in unrealized gains (losses) on available-for-sale securities, net of reclassification adjustment	1,450,865	4,293,680
Dividends declared, not yet paid	308,644	359,491
Derecognition of assets of consolidated VIEs	1,222,221	0
Derecognition of securitized debt of consolidated VIEs	$ 1,141,311	$ 0