Reinsurance (Components of Written Premiums) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Premiums Written, Net [Abstract]
Direct	$ 14,264	$ 13,587	$ 12,612
Assumed	281	303	279
Ceded	5,417	5,485	4,832
Net	9,128	8,405	8,059
Property and casualty
Premiums Written, Net [Abstract]
Direct	13,843	13,150	12,168
Assumed	235	255	229
Ceded	5,417	5,485	4,832
Net	8,661	7,920	7,565
Long term care
Premiums Written, Net [Abstract]
Direct	421	437	444
Assumed	46	48	50
Ceded	0	0	0
Net	$ 467	$ 485	$ 494
Percentage of assumed premiums written to net premiums written
Premiums Written, Net [Abstract]
Assumed/ Net %	3.10%	3.60%	3.50%
Percentage of assumed premiums written to net premiums written | Property and casualty
Premiums Written, Net [Abstract]
Assumed/ Net %	2.70%	3.20%	3.00%
Percentage of assumed premiums written to net premiums written | Long term care
Premiums Written, Net [Abstract]
Assumed/ Net %	9.90%	9.90%	10.10%