v3.26.3
Debt and letter of credit facilities - Letter of Credit Facilities (Details) - Standby letters of credit
Sep. 30, 2026
USD ($)
Line of Credit Facility [Line Items]  
Committed Capacity $ 255,000,000.0
Issued 761,300,000
Cash and Cash Equivalents  
Line of Credit Facility [Line Items]  
Collateral 23,000,000.0
Debt securities  
Line of Credit Facility [Line Items]  
Collateral 819,300,000
Committed - Secured letters of credit facilities  
Line of Credit Facility [Line Items]  
Committed Capacity 255,000,000.0
Issued 216,300,000
Committed - Secured letters of credit facilities | Cash and Cash Equivalents  
Line of Credit Facility [Line Items]  
Collateral 5,200,000
Committed - Secured letters of credit facilities | Debt securities  
Line of Credit Facility [Line Items]  
Collateral 128,100,000
Uncommitted - Secured letters of credit facilities  
Line of Credit Facility [Line Items]  
Issued 545,000,000.0
Uncommitted - Secured letters of credit facilities | Cash and Cash Equivalents  
Line of Credit Facility [Line Items]  
Collateral 17,800,000
Uncommitted - Secured letters of credit facilities | Debt securities  
Line of Credit Facility [Line Items]  
Collateral $ 691,200,000