Property and Casualty Insurance Reserves - Allowance for Credit Losses from Policyholders (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Liability for Future Policy Benefits and Unpaid Claims and Claims Adjustment Expense [Abstract]
Receivables from Policyholders (Allowance for Credit Losses: 2020 - $29.9; 2019 - $22.3)	$ 1,165.3	$ 1,165.3	$ 1,219.1	$ 1,117.1
Allowance for Expected Credit Losses
Balance at Beginning of Year	23.1	22.3
Current Period Change for Expected Credit Losses	15.9	27.8
Write-offs of Uncollectible Receivables from Policyholders	(9.1)	(20.2)
Balance at End of Period	$ 29.9	$ 29.9