Business and Summary of Significant Accounting Policies - Trade and Notes Receivable (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenue Recognition, Milestone Method [Line Items]
Insurance commissions as percentage of agent premiums	76.90%	77.10%	76.70%
Premium due from agents, net of accrued sales commissions	$ 35	$ 74
Minimum
Revenue Recognition, Milestone Method [Line Items]
Accrual for agency premiums reported within three months, percent	66.00%
Accrual for agency premiums reported within next three months, percent	6.00%
Accrual for agency premiums, time lag period	7 months
Maximum
Revenue Recognition, Milestone Method [Line Items]
Accrual for agency premiums reported within three months, percent	91.00%
Accrual for agency premiums reported within next three months, percent	17.00%
Accrual for agency premiums, time lag period	15 months