Cover Page
May 20, 2020
Document Information [Line Items]  
Document Type 8-K
Document Period End Date May 20, 2020
Entity Registrant Name Annaly Capital Management Inc
Entity Incorporation, State or Country Code MD
Entity File Number 1-13447
Entity Tax Identification Number 22-3479661
Entity Address, Address Line One 1211 Avenue of the Americas
Entity Address, City or Town New York,
Entity Address, State or Province NY
Entity Address, Postal Zip Code 10036
City Area Code 212
Local Phone Number 696-0100
Written Communications false
Soliciting Material false
Pre-commencement Tender Offer false
Pre-commencement Issuer Tender Offer false
Entity Emerging Growth Company false
Entity Central Index Key 0001043219
Amendment Flag false
Common Stock, par value $0.01 per share  
Document Information [Line Items]  
Title of 12(b) Security Common Stock, par value $0.01 per share
Trading Symbol NLY
Security Exchange Name NYSE
7.50% Series D Cumulative Redeemable Preferred Stock  
Document Information [Line Items]  
Title of 12(b) Security 7.50% Series D Cumulative Redeemable Preferred Stock
Trading Symbol NLY.D
Security Exchange Name NYSE
6.95% Series F Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock  
Document Information [Line Items]  
Title of 12(b) Security 6.95% Series F Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock
Trading Symbol NLY.F
Security Exchange Name NYSE
6.50% Series G Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock  
Document Information [Line Items]  
Title of 12(b) Security 6.50% Series G Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock
Trading Symbol NLY.G
Security Exchange Name NYSE
6.75% Series I Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock  
Document Information [Line Items]  
Title of 12(b) Security 6.75% Series I Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock
Trading Symbol NLY.I
Security Exchange Name NYSE