Principles of Consolidation And Other Matters (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 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	$ 201,000,000		$ 201,000,000		$ 197,000,000
Equity method investments lag period			3 months
Gain (loss) on investment income, net	(31,000,000)	$ 8,000,000	$ (33,000,000)	$ 13,000,000
Gain (loss) on equity securities	$ (2,000,000)	$ 3,000,000	$ (3,000,000)	$ 6,000,000
Effective tax rate (as a percent)	26.20%	37.40%	24.90%	28.20%
Unrecognized tax benefits	$ 79,000,000		$ 79,000,000		$ 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	12,000,000		12,000,000
Private Equity Funds
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Equity method income	(6,000,000)	$ 5,000,000	(7,000,000)	$ 7,000,000
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)