Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Revenue	$ 2,113	$ 2,048	$ 4,579	$ 4,360
Costs of providing services
Salaries and benefits	1,363	1,278	2,757	2,626
Other operating expenses	387	412	871	830
Depreciation	67	59	165	113
Amortization	119	123	240	250
Transaction and integration expenses	14	0	23	6
Total costs of providing services	1,950	1,872	4,056	3,825
Income from operations	163	176	523	535
Interest expense	(62)	(56)	(123)	(110)
Other income, net	76	67	168	122
INCOME FROM OPERATIONS BEFORE INCOME TAXES	177	187	568	547
Provision for income taxes	(75)	(38)	(153)	(105)
NET INCOME	102	149	415	442
Income attributable to non-controlling interests	(8)	(11)	(16)	(17)
NET INCOME ATTRIBUTABLE TO WILLIS TOWERS WATSON	$ 94	$ 138	$ 399	$ 425
EARNINGS PER SHARE
Basic earnings per share	$ 0.73	$ 1.06	$ 3.08	$ 3.27
Diluted earnings per share	$ 0.72	$ 1.06	$ 3.07	$ 3.26
Comprehensive income before non-controlling interests	$ 158	$ 132	$ 251	$ 447
Comprehensive income attributable to non-controlling interests	(8)	(13)	(15)	(18)
Comprehensive income attributable to Willis Towers Watson	$ 150	$ 119	$ 236	$ 429