Claim and Claim Adjustment Expense Reserves (Commercial - General Liability - 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, 2023	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, 2023	Dec. 31, 2023	Dec. 31, 2023	Dec. 31, 2023	Dec. 31, 2023	Dec. 31, 2023	Dec. 31, 2023	Dec. 31, 2023	Dec. 31, 2023
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total	$ 149	$ 67	$ 15
General Liability
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	151	74	13
Total net development for accident years prior to 2014	(2)	(7)	0
Total unallocated claim adjustment expense development	0	0	2
Total	149	67	15
General Liability | 2014
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	3	17	0	$ 1	$ 23	$ 4	$ (23)	$ (4)	$ 5									$ 26
General Liability | 2015
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	14	8	15	2	11	15	(2)	$ (5)									$ 58
General Liability | 2016
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	20	1	10	2	4	8	$ 36									$ 81
General Liability | 2017
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	38	22	(4)	2	0	$ 0									$ 58
General Liability | 2018
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	29	11	(7)	2	$ (9)									$ 26
General Liability | 2019
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	29	9	0	$ 2									$ 40
General Liability | 2020
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	10	4	$ (1)									$ 13
General Liability | 2021
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	9	$ 2									$ 11
General Liability | 2022
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Cumulative Number of Claims	$ (1)									$ (1)