DERIVATIVE INSTRUMENTS (Schedule of Derivative Instruments) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative asset fair value	$ 3,140	$ 18,875
Derivative liability fair value	18,382	11,486
Not Designated as Hedging Instruments \| Other assets
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative asset fair value	3,140	18,875
Not Designated as Hedging Instruments \| Other liabilities
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative liability fair value	18,382	11,486
Not Designated as Hedging Instruments \| Relating to investment portfolio: \| Foreign exchange forward contracts
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative notional amount	331,567	105,781
Not Designated as Hedging Instruments \| Relating to investment portfolio: \| Foreign exchange forward contracts \| Other assets
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative asset fair value	3,080	2
Not Designated as Hedging Instruments \| Relating to investment portfolio: \| Foreign exchange forward contracts \| Other liabilities
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative liability fair value	309	2,364
Not Designated as Hedging Instruments \| Relating to underwriting portfolio: \| Foreign exchange forward contracts
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative notional amount	1,118,590	1,197,012
Not Designated as Hedging Instruments \| Relating to underwriting portfolio: \| Foreign exchange forward contracts \| Other assets
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative asset fair value	60	18,873
Not Designated as Hedging Instruments \| Relating to underwriting portfolio: \| Foreign exchange forward contracts \| Other liabilities
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative liability fair value	9,956	0
Not Designated as Hedging Instruments \| Relating to underwriting portfolio: \| Other underwriting-related contracts
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative notional amount	75,000	75,000
Not Designated as Hedging Instruments \| Relating to underwriting portfolio: \| Other underwriting-related contracts \| Other assets
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative asset fair value	0	0
Not Designated as Hedging Instruments \| Relating to underwriting portfolio: \| Other underwriting-related contracts \| Other liabilities
Derivative Fair Values on Consolidated Balance Sheet [Line Items]
Derivative liability fair value	$ 8,117	$ 9,122

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226052-175313

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=123594938&loc=d3e13433-108611

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

+ Details

Name:	us-gaap_DerivativeAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=123594938&loc=d3e13433-108611

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226052-175313

+ Details

Name:	us-gaap_DerivativeLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL5579245-113959

+ Details

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

- 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

No definition available.

+ Details

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

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	axs_RelatedPortfolioAxis=axs_InvestmentPortfolioMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	axs_RelatedPortfolioAxis=axs_UnderwritingPortfolioMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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