Principles of Consolidation And Other Matters (Details) - USD ($)		3 Months Ended		6 Months Ended
	Jun. 10, 2021	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Revenue reduction for estimated commission revenue			$ 36,000,000
Operating funds related to regulatory requirements or as collateral under captive insurance arrangements		$ 304,000,000		$ 304,000,000		$ 270,000,000
Equity method investments lag period				3 months
Gain (loss) on investment income, net		$ 19,000,000	$ (31,000,000)	$ 30,000,000	$ (33,000,000)
Charge related to revaluation of deferred tax assets and liabilities	$ 100,000,000
Effective tax rate (as a percent)		31.60%	26.20%	27.90%	24.90%
Increase in effective tax rate due to change in U.K. corporate income tax rate, percent		8.30%		4.00%
Unrecognized tax benefits		$ 94,000,000		$ 94,000,000		$ 98,000,000
Minimum
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Reasonably possible decrease in unrecognized tax benefits		0		0
Maximum
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Reasonably possible decrease in unrecognized tax benefits		$ 33,000,000		$ 33,000,000
Alexander Forbes Group Holdings Limited
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Gain (loss) on investment income, net			$ (23,000,000)		$ (23,000,000)