Derivatives - Credit Risk Assumed through Credit Derivatives (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Credit Derivatives [Line Items]
Derivative, Notional Amount		$ 12,129	$ 13,706
Fair Value		(61)	(66)
Credit derivatives
Credit Derivatives [Line Items]
Derivative, Notional Amount		784	515
Fair Value		18	8
Offsetting Notional Amount		109	15
Offsetting Fair Value		3	5
Credit derivatives \| Single name credit default swaps \| A Minus \| Investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount		175	100
Fair Value		$ 9	3
Weighted Average Years to Maturity	5 years	5 years
Offsetting Notional Amount		$ 0	0
Offsetting Fair Value		0	0
Credit derivatives \| Basket credit default swaps \| BBB Plus \| Investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount		500	400
Fair Value		$ 12	10
Weighted Average Years to Maturity	5 years	5 years
Offsetting Notional Amount		$ 0	0
Offsetting Fair Value		0	0
Credit derivatives \| Basket credit default swaps \| Standard & Poor's, AAA Rating [Member] \| Investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount		100
Fair Value		$ 1
Weighted Average Years to Maturity		8 years
Offsetting Notional Amount		$ 100
Offsetting Fair Value		(1)
Credit derivatives \| Basket credit default swaps \| Standard & Poor's, CCC+ Rating \| Below investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount		9
Fair Value		$ (4)
Average Term of Credit Risk Derivatives Less than 1 Year		Less than 1 year
Offsetting Notional Amount		$ 9
Offsetting Fair Value		$ 4
Credit derivatives \| Basket credit default swaps \| A \| Investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount			1
Fair Value			0
Average Term of Credit Risk Derivatives Less than 1 Year	Less than 1 year
Offsetting Notional Amount			1
Offsetting Fair Value			0
Credit derivatives \| Basket credit default swaps \| CCC Minus \| Below investment grade risk exposure
Credit Derivatives [Line Items]
Derivative, Notional Amount			14
Fair Value			(5)
Average Term of Credit Risk Derivatives Less than 1 Year	Less than 1 year
Offsetting Notional Amount			14
Offsetting Fair Value			$ 5

Average Term of Credit Risk Derivatives Less than 1 Year

No definition available.

Name:	hig_AverageTermofCreditRiskDerivativesLessthan1Year
Namespace Prefix:	hig_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Derivative, Nominal Value, Amount Offset Against Collateral, Net

+ References

No definition available.

+ Details

Name:	hig_DerivativeNominalValueAmountOffsetAgainstCollateralNet
Namespace Prefix:	hig_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Average period covered by credit risk derivative contracts, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4K
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5708775-113959

+ Details

Name:	us-gaap_AverageTermOfCreditRiskDerivatives1
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

No definition available.

+ Details

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

- Definition

The net amount as of the balance sheet date of the fair value of derivative assets and derivative liabilities that in accordance with the entity's accounting policy were offset against collateral under a master netting arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=d3e41678-113959

+ Details

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

- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

Reference 1: 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=121572278&loc=d3e13433-108611

+ Details

Name:	us-gaap_DerivativeFairValueOfDerivativeNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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=121590274&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=121590274&loc=SL5579245-113959

+ Details

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

- Details

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

- Details

Name:	us-gaap_CreditDerivativesByContractTypeAxis=hig_SingleNameCreditDefaultSwapsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CreditRatingStandardPoorsAxis=srt_StandardPoorsAMinusRatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ExternalCreditRatingByGroupingAxis=us-gaap_ExternalCreditRatingInvestmentGradeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditDerivativesByContractTypeAxis=hig_BasketCreditDefaultSwapsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CreditRatingStandardPoorsAxis=srt_StandardPoorsBBBPlusRatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CreditRatingStandardPoorsAxis=srt_StandardPoorsAAARatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CreditRatingStandardPoorsAxis=srt_StandardPoorsCCCPlusRatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ExternalCreditRatingByGroupingAxis=us-gaap_ExternalCreditRatingNonInvestmentGradeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CreditRatingStandardPoorsAxis=srt_StandardPoorsARatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CreditRatingStandardPoorsAxis=srt_StandardPoorsCCCMinusRatingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: