v3.25.2
Debt and letter of credit facilities - Letter of Credit Facilities (Details) - Standby letters of credit
Jun. 30, 2025
USD ($)
Line of Credit Facility [Line Items]  
Issued $ 1,111,500,000
Cash and Cash Equivalents  
Line of Credit Facility [Line Items]  
Collateral 36,000,000.0
Debt securities  
Line of Credit Facility [Line Items]  
Collateral 1,303,500,000
Committed - Secured letters of credit facilities  
Line of Credit Facility [Line Items]  
Committed Capacity 390,000,000.0
Issued 278,000,000.0
Committed - Secured letters of credit facilities | Cash and Cash Equivalents  
Line of Credit Facility [Line Items]  
Collateral 15,900,000
Committed - Secured letters of credit facilities | Debt securities  
Line of Credit Facility [Line Items]  
Collateral 243,300,000
Uncommitted - Secured letters of credit facilities  
Line of Credit Facility [Line Items]  
Issued 833,500,000
Uncommitted - Secured letters of credit facilities | Cash and Cash Equivalents  
Line of Credit Facility [Line Items]  
Collateral 20,100,000
Uncommitted - Secured letters of credit facilities | Debt securities  
Line of Credit Facility [Line Items]  
Collateral $ 1,060,200,000