CAPITAL CONSTRUCTION FUND - CCF CASH and CASH EQUIVALENTS, and INVESTMENT ACCOUNT (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended
	Feb. 29, 2024	Sep. 30, 2025	Sep. 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 deposits into the CCF			50.0
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		168.4
Interest income on cash and cash equivalents, and CCF investments		13.4	14.9
Repurchase of assigned accounts receivable		100.7
Qualifying withdrawal payments for vessel construction expenditures		(136.5)	(35.8)
Total CCF cash and cash equivalents balance at end of period		376.7	178.7
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		(168.4)
Accretion of investments		7.7	8.6
Total CCF investments balance at end of period		251.2	456.7
Total CCF cash and cash equivalents, and investments balance at end of period		$ 627.9	$ 635.4	$ 642.6
Weighted average life of securities held within the fund		108 days
Capital construction fund, accrued interest on investments	$ 1.7
Debt security investments maturity term		2 years