Reinsurance (Components of 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
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
Long term care
Premiums Earned, Net [Abstract]
Direct	443	454	470
Assumed	48	50	50
Ceded	0	0	0
Net	$ 491	$ 504	$ 520
Percentage of assumed premiums earned to net premiums earned
Premiums Earned, Net [Abstract]
Assumed/ Net %	3.50%	3.80%	4.60%
Percentage of assumed premiums earned to net premiums earned | Property and casualty
Premiums Earned, Net [Abstract]
Assumed/ Net %	3.10%	3.30%	4.20%
Percentage of assumed premiums earned to net premiums earned | Long term care
Premiums Earned, Net [Abstract]
Assumed/ Net %	9.80%	9.90%	9.60%