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]	[1]	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)		$ 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		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)		11,526	48
Equity, ending balance (in shares) at Mar. 31, 2021			128,974
Equity, beginning balance at Dec. 31, 2021		13,308		10,804	4,645	(3)	(2,186)		13,260	48
Equity, beginning balance (in shares) at Dec. 31, 2021			122,056
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		125			122				122	3
Shares repurchased (in shares)			(9,860)
Shares repurchased		(2,250)			(2,250)				(2,250)
Dividends declared		(94)			(94)				(94)
Dividends attributable to non-controlling interests		(1)								(1)
Other comprehensive income (loss)		(56)					(56)		(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)		$ 11,004	$ 71
Equity, ending balance (in shares) at Mar. 31, 2022			112,213

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

[2] Attributable to the divestiture of our less than wholly-owned Miller subsidiary.