Claim and Claim Adjustment Expense Reserves (International - Excluding Hardy - 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
International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Total net liability for unpaid claim and claim adjustment expenses	2,276	2,003
Excluding Hardy | International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	2,128
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented	1,554
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2014	64
Liability for unallocated claim adjustment expenses for accident years presented	37
Total net liability for unpaid claim and claim adjustment expenses	1,655
Excluding Hardy | 2014 | International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	253	248	241	236	$ 203	$ 182	$ 166	$ 149	$ 121	$ 51
Excluding Hardy | 2015 | International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	246	237	230	219	204	182	162	132	$ 56
Excluding Hardy | 2016 | International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	237	226	214	192	180	158	131	$ 66
Excluding Hardy | 2017 | International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	321	264	237	214	186	146	$ 64
Excluding Hardy | 2018 | International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	308	266	242	212	166	$ 89
Excluding Hardy | 2019 | International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	247	224	201	164	$ 73
Excluding Hardy | 2020 | International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	178	162	128	$ 60
Excluding Hardy | 2021 | International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	154	124	$ 56
Excluding Hardy | 2022 | International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	138	$ 46
Excluding Hardy | 2023 | International
Short-Duration Insurance Contracts, Net Cumulative Paid Claim and Claim Adjustment Expenses [Line Items]
Cumulative paid claims and allocated claim adjustment expense, net	$ 46