Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Revenue	$ 8,998	$ 8,615	$ 8,370
Costs of providing services
Salaries and benefits	5,253	5,157	4,929
Other operating expenses	1,673	1,697	1,647
Depreciation	281	307	239
Amortization	369	461	488
Restructuring costs	26	24	0
Transaction and integration, net	(806)	110	13
Total costs of providing services	6,796	7,756	7,316
Income from operations	2,202	859	1,054
Interest expense	(211)	(244)	(234)
Other income, net	701	396	226
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	2,692	1,011	1,046
Provision for income taxes	(536)	(249)	(197)
INCOME FROM CONTINUING OPERATIONS	2,156	762	849
INCOME FROM DISCONTINUED OPERATIONS, NET OF TAX	2,080	258	224
NET INCOME	4,236	1,020	1,073
Income attributable to non-controlling interests	(14)	(24)	(29)
NET INCOME ATTRIBUTABLE TO WTW	$ 4,222	$ 996	$ 1,044
Basic earnings per share:
Income from continuing operations per share	$ 16.68	$ 5.69	$ 6.32
Income from discontinued operations per share	16.20	1.99	1.73
Basic earnings per share	32.88	7.68	8.05
Diluted earnings per share:
Income from continuing operations per share	16.63	5.67	6.30
Income from discontinued operations per share	16.15	1.98	1.72
Diluted earnings per share	$ 32.78	$ 7.65	$ 8.02
NET INCOME	$ 4,236	$ 1,020	$ 1,073
Other comprehensive (loss)/income, net of tax:
Foreign currency translation	(87)	139	78
Defined pension and post-retirement benefits	260	(266)	(329)
Derivative instruments	2	(4)	21
Other comprehensive income/(loss), net of tax, before non-controlling interests	175	(131)	(230)
Comprehensive income before non-controlling interests	4,411	889	843
Comprehensive income attributable to non-controlling interests	(16)	(25)	(29)
Comprehensive income attributable to WTW	$ 4,395	$ 864	$ 814