v3.25.2
CAPITAL CONSTRUCTION FUND - CCF CASH and CASH EQUIVALENTS, and INVESTMENT ACCOUNT (Details) - USD ($)
$ in Millions
 1 Months Ended 6 Months Ended
Feb. 29, 2024
Jun. 30, 2025
Jun. 30, 2024
Dec. 31, 2024
CCF Cash and Cash Equivalents:        
CCF cash and cash equivalents balance at beginning of period   $ 230.7 $ 599.4  
Cash withdrawal for the purchase of U.S. Treasury debt securities and accrued interest     (449.8)  
Proceeds from U.S. Treasury debt securities at maturity   91.1    
Interest income on cash and cash equivalents, and CCF investments   8.3 11.0  
Repurchase of assigned accounts receivable   100.7 35.8  
Qualifying withdrawal payments for vessel construction expenditures   (100.7) (35.8)  
Total CCF cash and cash equivalents balance at end of period   330.1 160.6  
CCF Investments:        
CCF investments balance at beginning of period   411.9    
Purchase of U.S. Treasury debt securities $ 448.1   448.1  
Sale of U.S. Treasury debt securities at maturity   (91.1)    
Accretion of investments   5.8 5.2  
Total CCF investments balance at end of period   326.6 453.3  
Total CCF cash and cash equivalents, and investments balance at end of period   $ 656.7 $ 613.9 $ 642.6
Weighted average life of securities held within the fund   99 days    
Capital construction fund, accrued interest on investments $ 1.7      
Debt security investments maturity term   2 years