Reinsurance, Effects of Reinsurance on Earned Premiums (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Premiums Earned, Net [Abstract]
Direct	$ 12,997	$ 12,001	$ 11,491
Assumed	288	288	338
Ceded	5,110	4,640	4,401
Net	$ 8,175	$ 7,649	$ 7,428
Assumed/Net %	3.50%	3.80%	4.60%
Direct and ceded earned premiums	$ 3,600	$ 3,500	$ 3,600
Percentage reinsured under significant third party captive program	100.00%
Reinsurance recoveries	$ 3,100	3,200	2,700
Property and casualty
Premiums Earned, Net [Abstract]
Direct	12,554	11,547	11,021
Assumed	240	238	288
Ceded	5,110	4,640	4,401
Net	$ 7,684	$ 7,145	$ 6,908
Assumed/Net %	3.10%	3.30%	4.20%
Long term care
Premiums Earned, Net [Abstract]
Direct	$ 443	$ 454	$ 470
Assumed	48	50	50
Ceded
Net	$ 491	$ 504	$ 520
Assumed/Net %	9.80%	9.90%	9.60%
Significant Third Party Captive Program
Premiums Earned, Net [Abstract]
Reinsurance recoveries	$ 2,000	$ 2,400	$ 2,100