Retirement Benefits - Fair Value Reconciliation (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Retirement Benefits [Abstract]
Net assets held in investments	$ 7,545	$ 7,400
Net receivable for investments purchased	0	2
Fair value of plan assets	$ 7,545	$ 7,402

Defined benefit plan fair value of plan assets liabilities reconciliation.

No definition available.

Name:	wtw_DefinedBenefitPlanFairValueOfPlanAssetsLiabilitiesReconciliation
Namespace Prefix:	wtw_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant