v3.22.2.2
Investments - Net Realized Gains (Losses), Including Impairment, Recognized in the Consolidated Statements of Operations (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2022
Sep. 30, 2021
Sep. 30, 2022
Sep. 30, 2021
Net realized (losses) gains on investments related to sales and other and fair value changes to equity securities:        
Total net realized (losses) gains on investments related to sales and other and fair value changes to equity securities $ (27.4) $ 112.1 $ (164.1) $ 123.0
Net realized (losses) gains related to impairments:        
Net realized losses related to impairments 0.0 0.0 (2.1) 0.2
Other investments 0.0 0.0 0.0 (1.0)
Total net realized (losses) gains on investments and fair value changes to equity securities (27.4) 112.1 (166.2) 123.2
Upward adjustment for equity securities under alternative measurement 0.0 23.0 19.5 25.1
Fixed maturity securities        
Net realized (losses) gains on investments related to sales and other and fair value changes to equity securities:        
Total net realized (losses) gains on investments related to sales and other and fair value changes to equity securities (21.9) 16.1 (63.0) 19.3
Net realized (losses) gains related to impairments:        
Net realized losses related to impairments 0.0 0.0 (1.6) 1.2
Equity securities        
Net realized (losses) gains on investments related to sales and other and fair value changes to equity securities:        
Total net realized (losses) gains on investments related to sales and other and fair value changes to equity securities (5.2) 95.1 (102.4) 100.6
Commercial mortgage loans on real estate        
Net realized (losses) gains on investments related to sales and other and fair value changes to equity securities:        
Total net realized (losses) gains on investments related to sales and other and fair value changes to equity securities (0.2) 0.5 0.0 0.7
Other investments        
Net realized (losses) gains on investments related to sales and other and fair value changes to equity securities:        
Total net realized (losses) gains on investments related to sales and other and fair value changes to equity securities (0.1) 0.4 1.3 2.4
Net realized (losses) gains related to impairments:        
Other investments $ 0.0 $ 0.0 $ (0.5) $ (1.0)