Long-Term Debt and Credit Facilities - Letters of Credit (Details)	Sep. 30, 2024 USD ($)
Long-term Debt and Credit Facilities
Letters of credit outstanding	$ 219,000,000
Uncommitted Letter of Credit Facility
Long-term Debt and Credit Facilities
Letters of credit outstanding	1,000,000
Facility Maintained By a Subsidiary
Long-term Debt and Credit Facilities
Letters of credit outstanding	2,000,000
Revolving Credit Facility
Long-term Debt and Credit Facilities
Letters of credit outstanding	216,000,000
Letter of Credit | Uncommitted Letter of Credit Facility
Long-term Debt and Credit Facilities
Maximum borrowing capacity	$ 225,000,000