NET INCOME (LOSS) PER COMMON SHARE - Schedule of Net Income (Loss) per Share Reconciliation (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income (loss)		$ 843,063	$ 82,351	$ 1,033,739	$ 538,692
Net income (loss) attributable to noncontrolling interests		10,618	15,906	19,971	18,838
Net income (loss) attributable to Annaly		832,445	66,445	1,013,768	519,854
Dividends on preferred stock	[1]	41,127	41,628	115,544	115,847
Net income (loss) available (related) to common stockholders		$ 791,318	$ 24,817	$ 898,224	$ 404,007
Weighted average shares of common stock outstanding-basic (in shares)		656,335,974	515,729,658	621,484,893	505,800,723
Add: Effect of stock awards, if dilutive (in shares)		1,520,453	1,102,494	1,283,588	817,420
Weighted average shares of common stock outstanding-diluted (in shares)		657,856,427	516,832,152	622,768,481	506,618,143
Net income (loss) per share available (related) to common share
Basic (in dollars per share)		$ 1.21	$ 0.05	$ 1.45	$ 0.80
Diluted (in dollars per share)		$ 1.20	$ 0.05	$ 1.44	$ 0.80
Series J Preferred Stock
Net income (loss) per share available (related) to common share
Cumulative and undeclared dividends		$ 3,700		$ 3,700

[1] (1) The three and nine months ended September 30, 2025 include cumulative and undeclared dividends of $3.7 million on the Company's 8.875% Series J Fixed-Rate Cumulative Redeemable Preferred Stock (the “Series J Preferred Stock”) as of September 30, 2025.