Debt and letter of credit facilities - Summary of letter of credit facilities (Details) - Standby letters of credit	Jun. 30, 2021 USD ($)
Line of Credit Facility
Issued	$ 1,078,000,000.0
Cash and Cash Equivalents
Line of Credit Facility
Collateral	613,600,000
Debt securities
Line of Credit Facility
Collateral	609,900,000
Committed - Secured letters of credit facilities
Line of Credit Facility
Committed Capacity	330,000,000.0
Issued	221,000,000.0
Committed - Secured letters of credit facilities \| Cash and Cash Equivalents
Line of Credit Facility
Collateral	126,500,000
Committed - Secured letters of credit facilities \| Debt securities
Line of Credit Facility
Collateral	0
Uncommitted - Secured letters of credit facilities
Line of Credit Facility
Issued	857,000,000.0
Uncommitted - Secured letters of credit facilities \| Cash and Cash Equivalents
Line of Credit Facility
Collateral	487,100,000
Uncommitted - Secured letters of credit facilities \| Debt securities
Line of Credit Facility
Collateral	$ 609,900,000

Amount of assets pledged to secure a debt instrument.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=123599511&loc=d3e64711-112823

+ Details

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

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_LineOfCreditFacilityLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_StandbyLettersOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_CashAndCashEquivalentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_DebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=spnt_CommittedSecuredLetterOfCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=spnt_UncommittedSecuredLetterOfCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: