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Investments Investments, held in Trust or on Deposit (Details) - USD ($)
$ in Millions
Dec. 31, 2021
Dec. 31, 2020
Deposit Assets [Abstract]    
Investments $ 2,736.0 $ 2,757.2
Assets Held-in-trust [Abstract]    
Funds held by or deposited with reinsurers 3.1 3.2
Required by various state laws and regulations to hold securities or letters of credit in depository account [Member]    
Deposit Assets [Abstract]    
Investments $ 861.4 $ 768.7