Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Revenue	$ 2,048	$ 1,990	$ 4,360	$ 4,282
Costs of providing services
Salaries and benefits	1,278	1,275	2,626	2,652
Other operating expenses	412	406	830	829
Depreciation	59	51	113	100
Amortization	123	140	250	281
Transaction and integration expenses	0	55	6	98
Total costs of providing services	1,872	1,927	3,825	3,960
Income from operations	176	63	535	322
Interest expense	(56)	(52)	(110)	(103)
Other income, net	67	63	122	119
INCOME FROM OPERATIONS BEFORE INCOME TAXES	187	74	547	338
Provision for income taxes	(38)	(9)	(105)	(52)
NET INCOME	149	65	442	286
Income attributable to non-controlling interests	(11)	(7)	(17)	(13)
NET INCOME ATTRIBUTABLE TO WILLIS TOWERS WATSON	$ 138	$ 58	$ 425	$ 273
EARNINGS PER SHARE
Basic earnings per share	$ 1.06	$ 0.44	$ 3.27	$ 2.06
Diluted earnings per share	$ 1.06	$ 0.44	$ 3.26	$ 2.05
Comprehensive income/(loss) before non-controlling interests	$ 132	$ (111)	$ 447	$ 194
Comprehensive income attributable to non-controlling interests	(13)	(6)	(18)	(13)
Comprehensive income/(loss) attributable to Willis Towers Watson	$ 119	$ (117)	$ 429	$ 181