CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net interest income
Interest income	$ 3,787,297,000	$ 3,332,563,000	$ 2,493,126,000
Interest expense	2,784,875,000	1,897,860,000	1,008,354,000
Net interest income	1,002,422,000	1,434,703,000	1,484,772,000
Realized and unrealized gains (losses)
Net interest component of interest rate swaps	351,375,000	100,553,000	(371,108,000)
Realized gains (losses) on termination or maturity of interest rate swaps	(1,442,964,000)	1,409,000	(160,133,000)
Unrealized gains (losses) on interest rate swaps	(1,210,276,000)	424,081,000	512,918,000
Subtotal	(2,301,865,000)	526,043,000	(18,323,000)
Net gains (losses) on disposal of investments	(47,944,000)	(1,124,448,000)	(3,938,000)
Net gains (losses) on other derivatives	(680,770,000)	(403,001,000)	261,438,000
Net unrealized gains (losses) on instruments measured at fair value through earnings	36,021,000	(158,082,000)	(39,684,000)
Loan loss provision	(16,569,000)	(3,496,000)	0
Subtotal	(709,262,000)	(1,689,027,000)	217,816,000
Total realized and unrealized gains (losses)	(3,011,127,000)	(1,162,984,000)	199,493,000
Other income (loss)	136,413,000	109,927,000	115,857,000
General and administrative expenses
Compensation and management fee	170,628,000	179,841,000	164,322,000
Other general and administrative expenses	131,006,000	150,032,000	59,802,000
Total general and administrative expenses	301,634,000	329,873,000	224,124,000
Income (loss) before income taxes	(2,173,926,000)	51,773,000	1,575,998,000
Income taxes	(10,835,000)	(2,375,000)	6,982,000
Net income (loss)	(2,163,091,000)	54,148,000	1,569,016,000
Net income (loss) attributable to noncontrolling interests	(226,000)	(260,000)	(588,000)
Net income (loss) attributable to Annaly	(2,162,865,000)	54,408,000	1,569,604,000
Dividends on preferred stock	136,576,000	129,312,000	109,635,000
Net income (loss) available (related) to common stockholders	$ (2,299,441,000)	$ (74,904,000)	$ 1,459,969,000
Net income (loss) per share available (related) to common stockholders
Basic (in dollars per share)	$ (1.60)	$ (0.06)	$ 1.37
Diluted (in dollars per share)	$ (1.60)	$ (0.06)	$ 1.37
Weighted average number of common shares outstanding
Basic (in shares)	1,434,912,682	1,209,601,809	1,065,923,652
Diluted (in shares)	1,434,912,682	1,209,601,809	1,066,351,616
Net income (loss)	$ (2,163,091,000)	$ 54,148,000	$ 1,569,016,000
Other comprehensive income (loss)
Unrealized gains (losses) on available-for-sale securities	4,135,862,000	(2,004,166,000)	(89,997,000)
Reclassification adjustment for net (gains) losses included in net income (loss)	(17,806,000)	1,150,321,000	49,870,000
Other comprehensive income (loss)	4,118,056,000	(853,845,000)	(40,127,000)
Comprehensive income (loss)	1,954,965,000	(799,697,000)	1,528,889,000
Comprehensive income (loss) attributable to noncontrolling interests	(226,000)	(260,000)	(588,000)
Comprehensive income (loss) attributable to Annaly	1,955,191,000	(799,437,000)	1,529,477,000
Dividends on preferred stock	136,576,000	129,312,000	109,635,000
Comprehensive income (loss) attributable to common stockholders	$ 1,818,615,000	$ (928,749,000)	$ 1,419,842,000