Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 31, 2018
Document And Entity Information [Abstract]
Document Type	10-Q/A
Amendment Flag	true
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Trading Symbol	NLY
Entity Registrant Name	ANNALY CAPITAL MANAGEMENT INC
Entity Central Index Key	0001043219
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		1,313,722,699
Amendment Description	Removed a header that was unintentionally included in the cover page of the initial filing. No other changes made to our Quarterly Report on Form 10-Q for the quarter ended September 30, 2018 that we filed with the Securities and Exchange Commission ("SEC") on November 2, 2018.