Reinsurance - Effects of Reinsurance on Earned Premiums (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Premiums Earned, Net [Abstract]
Direct	$ 13,524	$ 12,997	$ 12,001
Assumed	277	288	288
Ceded	5,134	5,110	4,640
Net	$ 8,667	$ 8,175	$ 7,649
Assumed/Net %	3.20%	3.50%	3.80%
Direct and ceded earned premiums	$ 3,300	$ 3,600	$ 3,500
Percentage reinsured under significant third party captive program	100.00%
Reinsurance recoveries	$ 2,600	3,100	3,200
Property and casualty
Premiums Earned, Net [Abstract]
Direct	13,097	12,554	11,547
Assumed	231	240	238
Ceded	5,134	5,110	4,640
Net	$ 8,194	$ 7,684	$ 7,145
Assumed/Net %	2.80%	3.10%	3.30%
Long term care
Premiums Earned, Net [Abstract]
Direct	$ 427	$ 443	$ 454
Assumed	46	48	50
Ceded
Net	$ 473	$ 491	$ 504
Assumed/Net %	9.70%	9.80%	9.90%
Significant Third Party Captive Program
Premiums Earned, Net [Abstract]
Reinsurance recoveries	$ 1,800	$ 2,000	$ 2,400