Document and Entity Information	3 Months Ended
	Mar. 31, 2013	May 06, 2013
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2013
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q1
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		947,368,897