DERIVATIVE INSTRUMENTS - Summary of Swaptions Outstanding (Details) - Notional - Long Positions - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2023	Dec. 31, 2022
Long pay
Derivative [Line Items]
Current Underlying Notional	$ 2,500,000	$ 2,500,000
Weighted Average Underlying Fixed Rate	2.02%	2.02%
Weighted Average Underlying Years to Maturity	7 years 8 months 8 days	8 years 2 months 8 days
Weighted Average Months to Expiration	8 months 9 days	1 year 2 months 9 days
Long receive
Derivative [Line Items]
Current Underlying Notional	$ 750,000	$ 750,000
Weighted Average Underlying Fixed Rate	1.57%	1.57%
Weighted Average Underlying Years to Maturity	10 years 6 months 25 days	11 years 25 days
Weighted Average Months to Expiration	6 months 25 days	1 year 25 days

Derivative Portfolio Expiration Period

No definition available.

Name:	nly_DerivativePortfolioExpirationPeriod
Namespace Prefix:	nly_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Interest rate swaptions weighted average underlying pay rate.

+ References

No definition available.

+ Details

Name:	nly_InterestRateSwaptionsWeightedAverageUnderlyingPayRate
Namespace Prefix:	nly_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Average remaining period until maturity of the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeAverageRemainingMaturity1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480237/815-40-50-5

+ Details

Name:	us-gaap_DerivativeLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-1B

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-1A

+ Details

Name:	us-gaap_DerivativeNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=nly_InterestRateSwaptionPayMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PositionAxis=us-gaap_LongMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=nly_InterestRateSwaptionReceiveMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: