Claim, Claim Adjustment Expense and Future Policy Benefit Reserves, General Liability (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) Claim	Dec. 31, 2020 USD ($)	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 ($)	Dec. 31, 2012 USD ($)
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2012	$ 3,830	$ 4,216	$ 4,584
Total net liability for unpaid claim and claim adjustment expenses	19,205	18,701	17,885	$ 17,965
Property and casualty
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total net liability for unpaid claim and claim adjustment expenses	15,270	14,195
General Liability
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	6,670
IBNR	2,006
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	3,929
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented	2,741
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2012	119
Liability for unallocated claim adjustment expenses for accident years presented	51
Total net liability for unpaid claim and claim adjustment expenses	2,911
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total net development for the accident years presented above	14	16	21
Total net development for accident years prior to 2012	(1)	(1)	(4)
Total unallocated claim adjustment expense development	2	0	(1)
Total	15	15	16
General Liability | Short-duration Insurance Contracts, Accident Year 2012
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	632	632	630	635	$ 635	$ 619	$ 636	$ 639	$ 611	$ 587
IBNR	$ 20
Cumulative number of claims | Claim	35,313
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 602	597	579	559	510	454	374	247	132	$ 28
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	0	2	(5)	0	16	(17)	(3)	28	24
IBNR, Total	45
General Liability | Short-duration Insurance Contracts, Accident Year 2013
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	624	623	620	623	613	655	650	655	650
IBNR	$ 24
Cumulative number of claims | Claim	33,706
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 582	572	551	510	450	352	240	128	$ 31
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	1	3	(3)	10	(42)	5	(5)	5
IBNR, Total	(26)
General Liability | Short-duration Insurance Contracts, Accident Year 2014
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	659	659	658	635	631	654	658	653
IBNR	$ 28
Cumulative number of claims | Claim	28,064
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 607	569	547	481	376	247	119	$ 31
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	0	1	23	4	(23)	(4)	5
IBNR, Total	6
General Liability | Short-duration Insurance Contracts, Accident Year 2015
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	617	602	600	589	574	576	581
IBNR	$ 42
Cumulative number of claims | Claim	24,118
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 530	501	446	357	230	110	$ 19
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	15	2	11	15	(2)	(5)
IBNR, Total	36
General Liability | Short-duration Insurance Contracts, Accident Year 2016
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	683	673	671	667	659	623
IBNR	$ 68
Cumulative number of claims | Claim	24,511
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 524	481	407	279	163	$ 32
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	10	2	4	8	36
IBNR, Total	60
General Liability | Short-duration Insurance Contracts, Accident Year 2017
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	630	634	632	632	632
IBNR	$ 67
Cumulative number of claims | Claim	22,195
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 471	399	250	118	$ 23
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(4)	2	0	0
IBNR, Total	(2)
General Liability | Short-duration Insurance Contracts, Accident Year 2018
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	639	646	644	653
IBNR	$ 205
Cumulative number of claims | Claim	19,917
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 307	228	107	$ 33
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(7)	2	(9)
IBNR, Total	(14)
General Liability | Short-Duration Insurance Contract, Accident Year 2019
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	682	682	680
IBNR	$ 330
Cumulative number of claims | Claim	18,602
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 181	98	$ 25
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	0	2
IBNR, Total	2
General Liability | Short-Duration Insurance Contract, Accident Year 2020
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	722	723
IBNR	$ 516
Cumulative number of claims | Claim	13,028
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 99	$ 23
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(1)
IBNR, Total	(1)
General Liability | Short-Duration Insurance Contract, Accident Year 2021
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	782
IBNR	$ 706
Cumulative number of claims | Claim	9,759
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 26