Claim and Claim Adjustment Expense Reserves and Future Policy Benefit Reserves - General Liability (Details) $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($) Claim	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2013	$ 4,348	$ 3,830	$ 4,216
Total net liability for unpaid claim and claim adjustment expenses	19,908	19,205	18,701	$ 17,885
Property and casualty
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total net liability for unpaid claim and claim adjustment expenses	15,996	15,270
General Liability
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	7,046
IBNR	2,324
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	4,017
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented	3,029
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2013	118
Liability for unallocated claim adjustment expenses for accident years presented	59
Total net liability for unpaid claim and claim adjustment expenses	3,206
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total net development for the accident years presented above	79	14	14
Total net development for accident years prior to 2013	(12)	(1)	1
Total unallocated claim adjustment expense development	0	2	0
Total	67	15	15
General Liability | Short-duration Insurance Contracts, Accident Year 2013
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	629	624	623	620	$ 623	$ 613	$ 655	$ 650	$ 655	$ 650
IBNR	$ 32
Cumulative number of claims | Claim	33,738
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 586	582	572	551	510	450	352	240	128	$ 31
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	5	1	3	(3)	10	(42)	5	(5)	5
IBNR, Total	(21)
General Liability | Short-duration Insurance Contracts, Accident Year 2014
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	676	659	659	658	635	631	654	658	653
IBNR	$ 34
Cumulative number of claims | Claim	28,131
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 624	607	569	547	481	376	247	119	$ 31
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	17	0	1	23	4	(23)	(4)	5
IBNR, Total	23
General Liability | Short-duration Insurance Contracts, Accident Year 2015
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	625	617	602	600	589	574	576	581
IBNR	$ 33
Cumulative number of claims | Claim	24,200
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 561	530	501	446	357	230	110	$ 19
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	8	15	2	11	15	(2)	(5)
IBNR, Total	44
General Liability | Short-duration Insurance Contracts, Accident Year 2016
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	684	683	673	671	667	659	623
IBNR	$ 43
Cumulative number of claims | Claim	24,699
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 582	524	481	407	279	163	$ 32
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	1	10	2	4	8	36
IBNR, Total	61
General Liability | Short-duration Insurance Contracts, Accident Year 2017
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	652	630	634	632	632	632
IBNR	$ 32
Cumulative number of claims | Claim	22,359
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 553	471	399	250	118	$ 23
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	22	(4)	2	0	0
IBNR, Total	20
General Liability | Short-duration Insurance Contracts, Accident Year 2018
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	650	639	646	644	653
IBNR	$ 127
Cumulative number of claims | Claim	20,242
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 428	307	228	107	$ 33
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	11	(7)	2	(9)
IBNR, Total	(3)
General Liability | Short-Duration Insurance Contract, Accident Year 2019
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	691	682	682	680
IBNR	$ 227
Cumulative number of claims | Claim	19,265
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 322	181	98	$ 25
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	9	0	2
IBNR, Total	11
General Liability | Short-Duration Insurance Contract, Accident Year 2020
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	726	722	723
IBNR	$ 434
Cumulative number of claims | Claim	13,998
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 192	99	$ 23
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	4	(1)
IBNR, Total	3
General Liability | Short-Duration Insurance Contract, Accident Year 2021
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	784	782
IBNR	$ 527
Cumulative number of claims | Claim	13,775
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 140	$ 26
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	2
IBNR, Total	2
General Liability | Short-Duration Insurance Contract, Accident Year 2022
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	929
IBNR	$ 835
Cumulative number of claims | Claim	10,572
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 29