Reinsurance (Components of Written Premiums) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Premiums Written, Net [Abstract]
Direct	$ 13,587	$ 12,612	$ 11,894
Assumed	303	279	331
Ceded	5,485	4,832	4,569
Net	8,405	8,059	7,656
Property and casualty
Premiums Written, Net [Abstract]
Direct	13,150	12,168	11,421
Assumed	255	229	281
Ceded	5,485	4,832	4,569
Net	7,920	7,565	7,133
Long term care
Premiums Written, Net [Abstract]
Direct	437	444	473
Assumed	48	50	50
Ceded	0	0	0
Net	$ 485	$ 494	$ 523
Percentage of assumed premiums written to net premiums written
Premiums Written, Net [Abstract]
Assumed/ Net %	3.60%	3.50%	4.30%
Percentage of assumed premiums written to net premiums written | Property and casualty
Premiums Written, Net [Abstract]
Assumed/ Net %	3.20%	3.00%	3.90%
Percentage of assumed premiums written to net premiums written | Long term care
Premiums Written, Net [Abstract]
Assumed/ Net %	9.90%	10.10%	9.60%