Investments Investments - Summary of Loan-To-Value and Average Debt-Service Coverage Ratios (Details) $ in Millions	12 Months Ended
Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Loans and Leases Receivable Disclosure [Line Items]
Fixed maturity securities on deposit with various governmental authorities	$ 370.1	$ 392.9
Geographic concentration risk \| California, Alabama and Utah \| Investment portfolio \| Commercial mortgage loans
Loans and Leases Receivable Disclosure [Line Items]
Concentration percentage	48.00%
Minimum \| Commercial mortgage loans
Loans and Leases Receivable Disclosure [Line Items]
Carrying Value	$ 0.2	0.1
Maximum \| Commercial mortgage loans
Loans and Leases Receivable Disclosure [Line Items]
Carrying Value	8.0	8.2
70% and less \| Commercial mortgage loans
Loans and Leases Receivable Disclosure [Line Items]
Carrying Value	$ 47.4	$ 54.6
% of Gross Mortgage Loans	100.00%	100.00%
Debt- Service Coverage Ratio	2.37	1.96
70% and less \| Maximum
Loans and Leases Receivable Disclosure [Line Items]
Loan-to-value percentage	70.00%	70.00%
Fixed maturity securities
Loans and Leases Receivable Disclosure [Line Items]
Fixed maturity securities on deposit with various governmental authorities	$ 6.5	$ 6.8

Represents the ratio of a loan underwritten to a value of an asset purchased.

No definition available.

Name:	tl_LoanToValuePercentage
Namespace Prefix:	tl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Loans and Leases Receivable, Debt Service Coverage Ratio

+ References

No definition available.

+ Details

Name:	tl_LoansandLeasesReceivableDebtServiceCoverageRatio
Namespace Prefix:	tl_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Loans and Leases Receivable, Percentage

+ References

No definition available.

+ Details

Name:	tl_LoansandLeasesReceivablePercentage
Namespace Prefix:	tl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Carrying amount of cash and investment securities on deposit with state regulatory authorities in connection with capital requirements.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 825
-Section 50
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=75763970&loc=SL75763979-209797

+ Details

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

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6351-108592

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13531-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13537-108611

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

+ Details

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
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

No definition available.

+ Details

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

- Definition

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=118952595&loc=d3e4428-111522

+ Details

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

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=us-gaap_GeographicConcentrationRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=tl_CaliforniaAlabamaandUtahMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=tl_InvestmentsTotalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=tl_LoanToValueSeventyPercentAndLessMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_FixedMaturitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: