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Employee Benefit Plans - Cash Flows (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016
Pension Benefits |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Employer contributions | $ 281 | $ 301
Other Postretirement Benefits |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Employer contributions | $ 0 | $ 0

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- Definition Defined Benefit Plan, Cash Paid for Contributions by Employer + References No definition available. + Details
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Namespace Prefix: | hig_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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

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- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |