Claim and Claim Adjustment Expense Reserves (Commercial - General Liability - Net Cumulative Paid Claim and Claim Adjustment Expenses) (Details) - USD ($) $ in Millions	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, 2014
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	$ 18,163	$ 16,929	$ 16,300	$ 15,857
Commercial
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	9,021	8,430
General Liability | Commercial
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	4,085
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented	3,554
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2014	162
Liability for unallocated claim adjustment expenses for accident years presented	64
Total net liability for unpaid claim and claim adjustment expenses	3,780
General Liability | Commercial | 2014
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	642	624	607	569	$ 547	$ 481	$ 376	$ 247	$ 119	$ 31
General Liability | Commercial | 2015
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	573	561	530	501	446	357	230	110	$ 19
General Liability | Commercial | 2016
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	620	582	524	481	407	279	163	$ 32
General Liability | Commercial | 2017
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	606	553	471	399	250	118	$ 23
General Liability | Commercial | 2018
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	491	428	307	228	107	$ 33
General Liability | Commercial | 2019
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	455	322	181	98	$ 25
General Liability | Commercial | 2020
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	280	192	99	$ 23
General Liability | Commercial | 2021
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	262	140	$ 26
General Liability | Commercial | 2022
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	123	$ 29
General Liability | Commercial | 2023
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	$ 33