Claim and Claim Adjustment Expense Reserves and Future Policy Benefit Reserves (Commercial - Commercial Auto - Net Strengthening or Releasing of Prior Accident Year Reserves) (Details) - Commercial - USD ($) $ in Millions	12 Months Ended									24 Months Ended	36 Months Ended	48 Months Ended	60 Months Ended	72 Months Ended	84 Months Ended	96 Months Ended	108 Months Ended	120 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2022	Dec. 31, 2022	Dec. 31, 2022	Dec. 31, 2022	Dec. 31, 2022	Dec. 31, 2022	Dec. 31, 2022	Dec. 31, 2022	Dec. 31, 2022
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total	$ 49	$ 53	$ 33
Commercial Auto
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	47	53	32
Total net development for accident years prior to 2013	2	0	1
Total unallocated claim adjustment expense development	0	0	0
Total	49	53	33
2013 | Commercial Auto
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	2	0	0	$ (4)	$ 0	$ (4)	$ (16)	$ 0	$ 19									$ (3)
2014 | Commercial Auto
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(1)	1	0	(4)	0	(7)	(11)	$ (11)									$ (33)
2015 | Commercial Auto
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	(1)	2	(2)	(7)	0	(9)	$ (2)									$ (19)
2016 | Commercial Auto
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	5	5	4	0	0	$ (12)									$ 2
2017 | Commercial Auto
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	7	11	21	2	$ (1)									$ 40
2018 | Commercial Auto
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	9	18	0	$ (2)									$ 25
2019 | Commercial Auto
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	34	23	$ 9									$ 66
2020 | Commercial Auto
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	1	$ (7)									$ (6)
2022 | Commercial Auto
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	$ (9)									$ (9)