Claim and Claim Adjustment Expense Reserves and Future Policy Benefit Reserves - Surety (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
Surety
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	801
IBNR	351
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	421
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented	380
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2013	(4)
Liability for unallocated claim adjustment expenses for accident years presented	20
Total net liability for unpaid claim and claim adjustment expenses	396
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total net development for the accident years presented above	(83)	(75)	(66)
Total net development for accident years prior to 2013	0	2	(3)
Total unallocated claim adjustment expense development	0	0	0
Total	(83)	(73)	(69)
Surety | Short-duration Insurance Contracts, Accident Year 2013
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	82	82	82	83	$ 87	$ 91	$ 106	$ 115	$ 121	$ 120
IBNR	$ 2
Cumulative number of claims | Claim	5,092
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 79	79	78	77	78	78	78	69	40	$ 16
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	0	0	(1)	(4)	(4)	(15)	(9)	(6)	1
IBNR, Total	(38)
Surety | Short-duration Insurance Contracts, Accident Year 2014
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	42	43	45	45	60	69	94	124	123
IBNR	$ 3
Cumulative number of claims | Claim	5,127
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 38	39	39	38	38	36	38	30	$ 7
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(1)	(2)	0	(15)	(9)	(25)	(30)	1
IBNR, Total	(81)
Surety | Short-duration Insurance Contracts, Accident Year 2015
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	45	53	58	63	79	104	131	131
IBNR	$ 1
Cumulative number of claims | Claim	5,074
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 42	42	44	42	40	38	26	$ 7
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(8)	(5)	(5)	(16)	(25)	(27)	0
IBNR, Total	(86)
Surety | Short-duration Insurance Contracts, Accident Year 2016
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	58	64	67	84	109	124	124
IBNR	$ 5
Cumulative number of claims | Claim	5,544
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 41	43	43	45	45	37	$ 5
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(6)	(3)	(17)	(25)	(15)	0
IBNR, Total	(66)
Surety | Short-duration Insurance Contracts, Accident Year 2017
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	66	71	84	103	115	120
IBNR	$ 4
Cumulative number of claims | Claim	5,855
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 62	49	46	41	37	$ 23
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(5)	(13)	(19)	(12)	(5)
IBNR, Total	(54)
Surety | Short-duration Insurance Contracts, Accident Year 2018
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	56	62	91	108	114
IBNR	$ 16
Cumulative number of claims | Claim	6,196
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 40	39	34	25	$ 5
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(6)	(29)	(17)	(6)
IBNR, Total	(58)
Surety | Short-Duration Insurance Contract, Accident Year 2019
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	87	98	112	119
IBNR	$ 21
Cumulative number of claims | Claim	6,033
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 59	44	34	$ 12
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(11)	(14)	(7)
IBNR, Total	(32)
Surety | Short-Duration Insurance Contract, Accident Year 2020
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	81	119	128
IBNR	$ 51
Cumulative number of claims | Claim	4,452
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 28	20	$ 4
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(38)	(9)
IBNR, Total	(47)
Surety | Short-Duration Insurance Contract, Accident Year 2021
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	129	137
IBNR	$ 105
Cumulative number of claims | Claim	4,168
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 20	$ 5
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(8)
IBNR, Total	(8)
Surety | Short-Duration Insurance Contract, Accident Year 2022
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	155
IBNR	$ 143
Cumulative number of claims | Claim	2,772
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 12