Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Revenue	$ 2,286	$ 2,113	$ 4,876	$ 4,579
Costs of providing services
Salaries and benefits	1,407	1,363	2,930	2,757
Other operating expenses	398	387	815	871
Depreciation	72	67	143	165
Amortization	98	119	201	240
Transaction and integration expenses	51	14	75	23
Total costs of providing services	2,026	1,950	4,164	4,056
Income from operations	260	163	712	523
Interest expense	(52)	(62)	(111)	(123)
Other income, net	74	76	513	168
INCOME FROM OPERATIONS BEFORE INCOME TAXES	282	177	1,114	568
Provision for income taxes	(96)	(75)	(192)	(153)
NET INCOME	186	102	922	415
Income attributable to non-controlling interests	(2)	(8)	(5)	(16)
NET INCOME ATTRIBUTABLE TO WILLIS TOWERS WATSON	$ 184	$ 94	$ 917	$ 399
EARNINGS PER SHARE
Basic earnings per share	$ 1.42	$ 0.73	$ 7.06	$ 3.08
Diluted earnings per share	$ 1.41	$ 0.72	$ 7.04	$ 3.07
Comprehensive income before non-controlling interests	$ 219	$ 158	$ 1,005	$ 251
Comprehensive income attributable to non-controlling interests	(2)	(8)	(7)	(15)
Comprehensive income attributable to Willis Towers Watson	$ 217	$ 150	$ 998	$ 236