Principles of Consolidation And Other Matters (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Operating funds related to regulatory requirements or as collateral under captive insurance arrangements	$ 247,000,000		$ 247,000,000		$ 197,000,000
Equity method investments lag period			3 months
Gain (loss) on investment income, net	(14,000,000)	$ 7,000,000	$ (47,000,000)	$ 20,000,000
Gain (loss) on equity securities	$ (16,000,000)	$ 4,000,000	$ (19,000,000)	$ 10,000,000
Effective tax rate (as a percent)	30.30%	26.00%	26.00%	27.80%
Unrecognized tax benefits	$ 102,000,000		$ 102,000,000		$ 86,000,000
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	22,000,000		22,000,000
Private Equity Funds
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Equity method income	$ 2,000,000	$ 3,000,000	(6,000,000)	$ 10,000,000
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)