Claim, Claim Adjustment Expense and Future Policy Benefit Reserves, Surety (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
Surety
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	765
IBNR	328
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	396
Net liability for unpaid claim and allocated claim adjustment expenses for the accident years presented	369
Net liability for unpaid claim and claim adjustment expenses for accident years prior to 2012	17
Liability for unallocated claim adjustment expenses for accident years presented	20
Total net liability for unpaid claim and claim adjustment expenses	406
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total net development for the accident years presented above	(76)	(67)	(79)
Total net development for accident years prior to 2012	3	(2)	(3)
Total unallocated claim adjustment expense development	0	0	(10)
Total	(73)	(69)	(92)
Surety | Short-duration Insurance Contracts, Accident Year 2012
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	36	37	38	39	$ 45	$ 52	$ 70	$ 98	$ 122	$ 120
IBNR	$ 1
Cumulative number of claims | Claim	5,586
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 36	36	37	37	36	35	35	34	32	$ 5
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(1)	(1)	(1)	(6)	(7)	(18)	(28)	(24)	2
IBNR, Total	(84)
Surety | Short-duration Insurance Contracts, Accident Year 2013
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	82	82	83	87	91	106	115	121	120
IBNR	$ 2
Cumulative number of claims | Claim	5,088
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 79	78	77	78	78	78	69	40	$ 16
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	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	43	45	45	60	69	94	124	123
IBNR	$ 1
Cumulative number of claims | Claim	5,118
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 39	39	38	38	36	38	30	$ 7
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(2)	0	(15)	(9)	(25)	(30)	1
IBNR, Total	(80)
Surety | Short-duration Insurance Contracts, Accident Year 2015
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	53	58	63	79	104	131	131
IBNR	$ 9
Cumulative number of claims | Claim	5,055
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 42	44	42	40	38	26	$ 7
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(5)	(5)	(16)	(25)	(27)	0
IBNR, Total	(78)
Surety | Short-duration Insurance Contracts, Accident Year 2016
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	64	67	84	109	124	124
IBNR	$ 10
Cumulative number of claims | Claim	5,521
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 43	43	45	45	37	$ 5
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(3)	(17)	(25)	(15)	0
IBNR, Total	(60)
Surety | Short-duration Insurance Contracts, Accident Year 2017
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	71	84	103	115	120
IBNR	$ 9
Cumulative number of claims | Claim	5,795
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 49	46	41	37	$ 23
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(13)	(19)	(12)	(5)
IBNR, Total	(49)
Surety | Short-duration Insurance Contracts, Accident Year 2018
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	62	91	108	114
IBNR	$ 19
Cumulative number of claims | Claim	6,097
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 39	34	25	$ 5
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(29)	(17)	(6)
IBNR, Total	(52)
Surety | Short-Duration Insurance Contract, Accident Year 2019
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	98	112	119
IBNR	$ 44
Cumulative number of claims | Claim	5,816
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 44	34	$ 12
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(14)	(7)
IBNR, Total	(21)
Surety | Short-Duration Insurance Contract, Accident Year 2020
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	119	128
IBNR	$ 104
Cumulative number of claims | Claim	4,006
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 20	$ 4
Net Strengthening (Releases) of Prior Accident Year Reserves [Abstract]
Total	(9)
IBNR, Total	(9)
Surety | Short-Duration Insurance Contract, Accident Year 2021
Cumulative Net Incurred Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	137
IBNR	$ 129
Cumulative number of claims | Claim	2,592
Cumulative Net Paid Claim and Allocated Claim Adjustment Expenses [Abstract]
Total	$ 5