Claim and Claim Adjustment Expense Reserves and Future Policy Benefit Reserves (Specialty - Surety - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - Surety - Specialty $ in Millions	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 ($)	Dec. 31, 2013 USD ($)
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 801
IBNR	351
2013
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	82	$ 82	$ 82	$ 83	$ 87	$ 91	$ 106	$ 115	$ 121	$ 120
IBNR	$ 2
Cumulative Number of Claims | claim	5,092
2014
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 42	43	45	45	60	69	94	124	$ 123
IBNR	$ 3
Cumulative Number of Claims | claim	5,127
2015
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 45	53	58	63	79	104	131	$ 131
IBNR	$ 1
Cumulative Number of Claims | claim	5,074
2016
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 58	64	67	84	109	124	$ 124
IBNR	$ 5
Cumulative Number of Claims | claim	5,544
2017
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 66	71	84	103	115	$ 120
IBNR	$ 4
Cumulative Number of Claims | claim	5,855
2018
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 56	62	91	108	$ 114
IBNR	$ 16
Cumulative Number of Claims | claim	6,196
2019
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 87	98	112	$ 119
IBNR	$ 21
Cumulative Number of Claims | claim	6,033
2020
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 81	119	$ 128
IBNR	$ 51
Cumulative Number of Claims | claim	4,452
2021
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 129	$ 137
IBNR	$ 105
Cumulative Number of Claims | claim	4,168
2022
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 155
IBNR	$ 143
Cumulative Number of Claims | claim	2,772