Retirement Benefits - Benefit Obligation In Excess Of Plan Assets (Details) - Pension Plan [Member] - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
United States [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation at end of year	$ 4,098	$ 939
Fair value of plan assets at end of year	3,803	713
United Kingdom [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation at end of year	5	5
Fair value of plan assets at end of year	0	0
Other Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation at end of year	324	278
Fair value of plan assets at end of year	$ 182	$ 145

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.

No definition available.

+ Details

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

- Definition

Amount of plan asset for defined benefit pension plan with projected benefit obligation in excess of plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480482/715-20-55-17

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-3

+ Details

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

- Definition

Amount of projected benefit obligation for defined benefit pension plan with projected benefit obligation in excess of plan assets.

+ References

+ Details

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

- Details

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

- Details

Name:	us-gaap_RetirementPlanSponsorLocationAxis=country_US
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanSponsorLocationAxis=country_GB
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RetirementPlanSponsorLocationAxis=wtw_OtherForeignPlansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: