Condensed Consolidated Statements of Changes in Equity (Unaudited) - USD ($) $ in Millions		Total	Shares outstanding [Member]	Ordinary shares and APIC [Member]	Retained earnings (accumulated deficit) [Member]	Treasury Shares [Member]	AOCL [Member]		Total WTW shareholders' equity [Member]	Non-controlling interests [Member]
Equity, beginning balance at Dec. 31, 2023		$ 9,593		$ 10,910	$ 1,466		$ (2,856)	[1]	$ 9,520	$ 73
Equity, beginning balance (in shares) at Dec. 31, 2023			102,538,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares repurchased		(101)			(101)				(101)
Shares repurchased (in shares)			(374,000)
Net (loss)/income		194			190				190	4
Dividends declared		(91)			(91)				(91)
Dividends attributable to non-controlling interests		(1)								(1)
Other comprehensive (loss)/income		(49)					(49)	[1]	(49)
Issuance of shares under employee stock compensation plans (in shares)			49,000
Share-based compensation and net settlements		16		16					16
Additional non-controlling interests	[2]	3								3
Foreign currency translation		4		4					4
Equity, ending balance at Mar. 31, 2024		9,568		10,930	1,464		(2,905)	[1]	9,489	79
Equity, ending balance (in shares) at Mar. 31, 2024			102,213,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares repurchased		(200)			(200)				(200)
Shares repurchased (in shares)			(775,000)
Net (loss)/income		142			141				141	1
Dividends declared		(90)			(90)				(90)
Dividends attributable to non-controlling interests		(2)								(2)
Other comprehensive (loss)/income		(16)					(16)	[1]	(16)
Issuance of shares under employee stock compensation plans (in shares)			109,000
Share-based compensation and net settlements		12		12					12
Foreign currency translation		1		1					1
Equity, ending balance at Jun. 30, 2024		9,415		10,943	1,315		(2,921)	[1]	9,337	78
Equity, ending balance (in shares) at Jun. 30, 2024			101,547,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares repurchased		(205)			(200)	$ (5)			(205)
Shares repurchased (in shares)			(717,000)
Net (loss)/income		(1,672)			(1,675)				(1,675)	3
Dividends declared		(90)			(90)				(90)
Dividends attributable to non-controlling interests		(3)								(3)
Other comprehensive (loss)/income		111					111	[1]	111
Issuance of shares under employee stock compensation plans (in shares)			41,000
Share-based compensation and net settlements		23		23					23
Reduction of non-controlling interests	[2]	(4)		(4)					(4)
Foreign currency translation		(5)		(5)					(5)
Equity, ending balance at Sep. 30, 2024		7,570		10,957	(650)	$ (5)	(2,810)	[1]	7,492	78
Equity, ending balance (in shares) at Sep. 30, 2024			100,871,000
Equity, beginning balance at Dec. 31, 2024		8,017		10,989	109		(3,158)	[3]	7,940	77
Equity, beginning balance (in shares) at Dec. 31, 2024			99,806,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares repurchased		(200)			(200)				(200)
Shares repurchased (in shares)			(607,000)
Net (loss)/income		239			235				235	4
Dividends declared		(93)			(93)				(93)
Other comprehensive (loss)/income		223					223	[3]	223
Issuance of shares under employee stock compensation plans (in shares)			12,000
Share-based compensation and net settlements		33		33					33
Foreign currency translation		(5)		(5)					(5)
Equity, ending balance at Mar. 31, 2025		8,214		11,017	51		(2,935)	[3]	8,133	81
Equity, ending balance (in shares) at Mar. 31, 2025			99,211,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares repurchased		(500)			(500)				(500)
Shares repurchased (in shares)			(1,615,000)
Net (loss)/income		332			331				331	1
Dividends declared		(88)			(88)				(88)
Dividends attributable to non-controlling interests		(2)								(2)
Other comprehensive (loss)/income		229					229	[3]	229
Issuance of shares under employee stock compensation plans (in shares)			257,000
Share-based compensation and net settlements		5		5					5
Foreign currency translation		(10)		(10)					(10)
Equity, ending balance at Jun. 30, 2025		8,180		11,012	(206)		(2,706)	[3]	8,100	80
Equity, ending balance (in shares) at Jun. 30, 2025			97,853,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares repurchased		(600)			(600)				(600)
Shares repurchased (in shares)			(1,848,000)
Net (loss)/income		306			304				304	2
Dividends declared		(91)			(91)				(91)
Dividends attributable to non-controlling interests		(4)								(4)
Other comprehensive (loss)/income		(3)					(3)	[3]	(3)
Issuance of shares under employee stock compensation plans (in shares)			42,000
Share-based compensation and net settlements		26		26					26
Reduction of non-controlling interests	[4]	(3)								(3)
Foreign currency translation		(1)		(1)					(1)
Equity, ending balance at Sep. 30, 2025		$ 7,810		$ 11,037	$ (593)		$ (2,709)	[3]	$ 7,735	$ 75
Equity, ending balance (in shares) at Sep. 30, 2025			96,047,000

[1] Accumulated other comprehensive loss, net of tax (‘AOCL’).

[2] Attributable to the divestiture of businesses that are less than wholly-owned or the acquisition of shares previously owned by minority interest holders. In an acquisition, additional paid-in capital is adjusted as well to the extent that the consideration transferred differs from the carrying value of non-controlling interests prior to the acquisition.

[3] Accumulated other comprehensive loss, net of tax (‘AOCL’).

[4] Attributable to the divestiture of businesses that are less than wholly-owned or the acquisition of shares previously owned by minority interest holders. In an acquisition, additional paid-in capital is adjusted as well to the extent that the consideration transferred differs from the carrying value of non-controlling interests prior to the acquisition.