Condensed Consolidated Statements of Changes in Equity (Unaudited) - USD ($) shares in Thousands, $ in Millions		Total	Shares outstanding [Member]	Ordinary shares and APIC [Member]	Retained earnings [Member]	Treasury shares [Member]	AOCL [Member]		Total WTW shareholders' equity [Member]	Non-controlling interests [Member]
Equity, beginning balance at Dec. 31, 2020		$ 10,932		$ 10,748	$ 2,434	$ (3)	$ (2,359)	[1]	$ 10,820	$ 112
Equity, beginning balance (in shares) at Dec. 31, 2020			128,965
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		736			733				733	3
Dividends declared		(92)			(92)				(92)
Dividends attributable to non-controlling interests		(17)								(17)
Other comprehensive income (loss)		50					48	[1]	48	2
Issuance of shares under employee stock compensation plans		1		1					1
Issuance of shares under employee stock compensation plans (in shares)			9
Share-based compensation and net settlements		12		12					12
Reduction of non-controlling interests	[2]	(52)								(52)
Foreign currency translation		4		4					4
Equity, ending balance at Mar. 31, 2021		11,574		10,765	3,075	(3)	(2,311)	[1]	11,526	48
Equity, ending balance (in shares) at Mar. 31, 2021			128,974
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		186			184				184	2
Dividends declared		(93)			(93)				(93)
Dividends attributable to non-controlling interests		(4)								(4)
Other comprehensive income (loss)		33					33	[1]	33
Issuance of shares under employee stock compensation plans		1		1					1
Issuance of shares under employee stock compensation plans (in shares)			14
Share-based compensation and net settlements		20		20					20
Reduction of non-controlling interests	[2]	(1)								(1)
Foreign currency translation		(1)		(1)					(1)
Equity, ending balance at Jun. 30, 2021		11,715		10,785	3,166	(3)	(2,278)	[1]	11,670	45
Equity, ending balance (in shares) at Jun. 30, 2021			128,988
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares repurchased (in shares)			(4,456)
Shares repurchased		(1,000)			(1,000)				(1,000)
Net income		907			903				903	4
Dividends declared		(100)			(100)				(100)
Dividends attributable to non-controlling interests		(6)								(6)
Other comprehensive income (loss)		(81)					(81)		(81)
Issuance of shares under employee stock compensation plans (in shares)			64
Share-based compensation and net settlements		6		6					6
Reduction of non-controlling interests	[2]	(11)		(8)					(8)	(3)
Foreign currency translation		3		3					3
Equity, ending balance at Sep. 30, 2021		11,433		10,786	2,969	(3)	(2,359)		11,393	40
Equity, ending balance (in shares) at Sep. 30, 2021			124,596
Equity, beginning balance at Dec. 31, 2021		13,308		10,804	4,645	(3)	(2,186)	[1]	13,260	48
Equity, beginning balance (in shares) at Dec. 31, 2021			122,056
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares repurchased (in shares)			(9,860)
Shares repurchased		(2,250)			(2,250)				(2,250)
Net income		125			122				122	3
Dividends declared		(94)			(94)				(94)
Dividends attributable to non-controlling interests		(1)								(1)
Other comprehensive income (loss)		(56)					(56)	[1]	(56)
Issuance of shares under employee stock compensation plans		1		1					1
Issuance of shares under employee stock compensation plans (in shares)			17
Share-based compensation and net settlements		20		20					20
Acquisition of non-controlling interests		21								21
Foreign currency translation		1		1					1
Equity, ending balance at Mar. 31, 2022		11,075		10,826	2,423	(3)	(2,242)	[1]	11,004	71
Equity, ending balance (in shares) at Mar. 31, 2022			112,213
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares repurchased (in shares)			(2,144)
Shares repurchased		(471)			(471)				(471)
Net income		114			109				109	5
Dividends declared		(90)			(90)				(90)
Dividends attributable to non-controlling interests		(2)								(2)
Other comprehensive income (loss)		(244)					(244)	[1]	(244)
Issuance of shares under employee stock compensation plans (in shares)			27
Share-based compensation and net settlements		22		22					22
Sale of non-controlling interests		6								6
Foreign currency translation		7		7					7
Equity, ending balance at Jun. 30, 2022		10,417		10,855	1,971	(3)	(2,486)	[1]	10,337	80
Equity, ending balance (in shares) at Jun. 30, 2022			110,096
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares repurchased (in shares)			(1,789)
Shares repurchased		(369)			(369)				(369)
Net income		192			190				190	2
Dividends declared		(86)			(86)				(86)
Dividends attributable to non-controlling interests		(5)								(5)
Other comprehensive income (loss)		(234)					(234)		(234)
Issuance of shares under employee stock compensation plans		6		6					6
Issuance of shares under employee stock compensation plans (in shares)			355
Share-based compensation and net settlements		(14)		(14)					(14)
Acquisition of non-controlling interests				2					2	(2)
Foreign currency translation		6		6					6
Equity, ending balance at Sep. 30, 2022		$ 9,913		$ 10,855	$ 1,706	$ (3)	$ (2,720)		$ 9,838	$ 75
Equity, ending balance (in shares) at Sep. 30, 2022			108,662

[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.