v3.26.1
Debt and letter of credit facilities - Letter of Credit Facilities (Details) - Standby letters of credit
Jun. 30, 2026
USD ($)
Line of Credit Facility [Line Items]  
Committed Capacity $ 330,000,000.0
Issued 810,000,000.0
Cash and Cash Equivalents  
Line of Credit Facility [Line Items]  
Collateral 39,500,000
Debt securities  
Line of Credit Facility [Line Items]  
Collateral 839,900,000
Committed - Secured letters of credit facilities  
Line of Credit Facility [Line Items]  
Committed Capacity 330,000,000.0
Issued 219,600,000
Committed - Secured letters of credit facilities | Cash and Cash Equivalents  
Line of Credit Facility [Line Items]  
Collateral 3,200,000
Committed - Secured letters of credit facilities | Debt securities  
Line of Credit Facility [Line Items]  
Collateral 131,600,000
Uncommitted - Secured letters of credit facilities  
Line of Credit Facility [Line Items]  
Issued 590,400,000
Uncommitted - Secured letters of credit facilities | Cash and Cash Equivalents  
Line of Credit Facility [Line Items]  
Collateral 36,300,000
Uncommitted - Secured letters of credit facilities | Debt securities  
Line of Credit Facility [Line Items]  
Collateral $ 708,300,000