Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Revenue	$ 2,312	$ 2,292
Costs of providing services
Salaries and benefits	1,348	1,377
Other operating expenses	418	423
Depreciation	54	49
Amortization	127	141
Transaction and integration expenses	6	43
Total costs of providing services	1,953	2,033
Income from operations	359	259
Interest expense	(54)	(51)
Other income, net	55	56
INCOME FROM OPERATIONS BEFORE INCOME TAXES	360	264
Provision for income taxes	(67)	(43)
NET INCOME	293	221
Income attributable to non-controlling interests	(6)	(6)
NET INCOME ATTRIBUTABLE TO WILLIS TOWERS WATSON	$ 287	$ 215
EARNINGS PER SHARE
Basic earnings per share	$ 2.21	$ 1.62
Diluted earnings per share	$ 2.20	$ 1.61
Comprehensive income before non-controlling interests	$ 315	$ 305
Comprehensive income attributable to non-controlling interests	(5)	(7)
Comprehensive income attributable to Willis Towers Watson	$ 310	$ 298