XML 75 R57.htm IDEA: XBRL DOCUMENT
v3.20.4

SECURITIES - Additional Information (Details) - USD ($) $ in Billions | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2020 | Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract] |  |
Residential investment securities sold, carrying value | $ 25.5 | $ 51.8

X
- Definition Carrying value of mortgage backed securities sold during period. + References No definition available. + Details
Name: | nly_MortgageBackedSecuritiesSoldCarryingValue
Namespace Prefix: | nly_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration