XML 148 R97.htm IDEA: XBRL DOCUMENT v3.24.3
Investments - Net Realized and Unrealized Investment Gains and Losses and Change in Unrealized Gains and Losses on Investments (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2024
Sep. 30, 2023
Sep. 30, 2024
Sep. 30, 2023
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Schedule of Investment Income, Reported Amounts, by Category [Line Items]              
Fixed income securities - gross realized gains $ 1.0 $ 0.0 $ 1.4 $ 0.4 $ 1.6 $ 2.9 $ 22.7
Fixed income securities - gross realizes (losses) (10.9) (8.6) (36.1) (15.6) (41.5) (58.4) (3.6)
Net change in expected credit gains (losses) 0.5 0.3 0.9 4.0 4.8 (5.0) (2.5)
Fixed income securities, trading - gross realized gains         1.0 0.2 12.2
Fixed income securities, trading, gross realizes (losses)         (3.5) (1.8) (2.0)
Privately-held investments net unrealized gains/(losses)         65.9 (113.9) (23.4)
Catastrophe bonds 0.0 0.1 0.0 (0.5) 0.1 0.2 (0.8)
Total net realized and unrealized investment (losses)/gains recorded in the consolidated statement of operations 6.1 (1.8) (21.0) 16.2 14.5 (177.6) 8.8
Change in available for sale net unrealized (losses)/gains:              
Fixed income securities 120.7 (45.0) 103.6 (32.7) 126.2 (391.7) (157.6)
Income tax benefit/(expense)         (20.6) 23.9 (0.3)
Total change in net unrealized (losses)/gains, net of taxes recorded in other comprehensive income         105.6 (367.8) (157.9)
Privately-held investments              
Schedule of Investment Income, Reported Amounts, by Category [Line Items]              
Fixed income securities, trading - gross realized gains 0.1 0.2 0.6 0.3 0.8 0.7 0.6
Fixed income securities, trading, gross realizes (losses) (14.3) 0.0 (14.6) 0.0 0.0 (0.1) (13.8)
Privately-held investments net unrealized gains/(losses) 9.5 (4.1) (8.0) (13.1) (15.2) (2.5) 18.1
Short-term investments              
Schedule of Investment Income, Reported Amounts, by Category [Line Items]              
Fixed income securities - gross realized gains 0.5 0.0 0.7 0.1 0.6 1.0 2.0
Fixed income securities - gross realizes (losses) 0.0 0.0 (1.4) (0.3) (0.9) (0.5) (0.8)
Fixed income securities, trading - gross realized gains 0.0 0.0 0.0 0.1 0.1 0.0 0.1
Fixed income securities, trading, gross realizes (losses) 0.0 0.0 (0.2) (0.2) (0.3) 0.0 (0.3)
MVI              
Schedule of Investment Income, Reported Amounts, by Category [Line Items]              
Income/(loss) from equity method investment         0.2 0.0 0.1
Multi-Line Insurer              
Schedule of Investment Income, Reported Amounts, by Category [Line Items]              
Income/(loss) from equity method investment $ 0.3 $ 0.4 $ 0.5 $ 0.8 $ 0.8 $ (0.4) $ 0.2