Nature of Operations (Details) numberOfColleague in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) numberOfColleague country	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) numberOfColleague country	Sep. 30, 2019 USD ($)
Nature of Operations [Line Items]
Entity number of colleagues | numberOfColleague	76		76
Revenue	$ 3,968	$ 3,968	$ 12,808	$ 12,388
Number of countries in which entity operates (more than) | country	130		130
Marsh & McLennan Companies, Inc.
Nature of Operations [Line Items]
Revenue			$ 17,000