v3.26.3
Variable and voting interest entities - Narrative (Details) - USD ($)
$ in Millions
 9 Months Ended
Sep. 30, 2026
Dec. 31, 2025
Variable Interest Entity [Line Items]    
Assets $ 12,622.3 $ 12,569.6
Liabilities 10,392.9 10,098.7
Third Point Venture Offshore Fund I LP    
Variable Interest Entity [Line Items]    
Unfunded commitments 5.9 7.1
Third Point Venture Offshore Fund II LP    
Variable Interest Entity [Line Items]    
Unfunded commitments 16.0 18.2
Third Point Insurance Solutions Fund I LLC    
Variable Interest Entity [Line Items]    
Unfunded commitments 10.4 25.0
Variable Interest Entity, Primary Beneficiary, Alstead Re Insurance Company    
Variable Interest Entity [Line Items]    
Assets 9.0 6.8
Liabilities 3.2 0.9
Alta Signa    
Variable Interest Entity [Line Items]    
Assets 2.1 1.8
Liabilities $ 1.2 $ 1.3
VOE, ownership percentage 75.10%  
TP Enhanced Fund | TP Enhanced Fund    
Variable Interest Entity [Line Items]    
VIE, ownership percentage 89.00%  
Variable interest entity, primary beneficiary | TP Enhanced Fund | TP GP    
Variable Interest Entity [Line Items]    
VIE, ownership percentage 11.00%