Claim and Claim Adjustment Expense Reserves and Future Policy Benefit Reserves (Commercial - Workers' Compensation - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - Workers' Compensation - Commercial $ 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	$ 4,298
IBNR	1,286
2013
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	537	$ 548	$ 552	$ 561	$ 582	$ 593	$ 618	$ 592	$ 572	$ 537
IBNR	$ 82
Cumulative Number of Claims | claim	38,979
2014
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 430	448	439	446	450	452	479	480	$ 467
IBNR	$ 76
Cumulative Number of Claims | claim	33,522
2015
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 353	372	382	394	408	406	431	$ 422
IBNR	$ 80
Cumulative Number of Claims | claim	31,899
2016
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 331	355	366	382	396	405	$ 426
IBNR	$ 77
Cumulative Number of Claims | claim	31,991
2017
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 399	402	400	421	432	$ 440
IBNR	$ 81
Cumulative Number of Claims | claim	33,130
2018
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 415	415	428	440	$ 450
IBNR	$ 93
Cumulative Number of Claims | claim	34,875
2019
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 436	437	449	$ 452
IBNR	$ 105
Cumulative Number of Claims | claim	34,324
2020
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 446	466	$ 477
IBNR	$ 182
Cumulative Number of Claims | claim	29,392
2021
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 454	$ 468
IBNR	$ 202
Cumulative Number of Claims | claim	29,886
2022
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 497
IBNR	$ 308
Cumulative Number of Claims | claim	28,753