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Commitments and Contingencies - Contingent obligation (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) paymentInstallment	Dec. 31, 2022 USD ($)
Debt Instrument [Line Items]
Contingent obligation	$ 0.0	$ 0.0
E.ON Contingent Obligation | Other Liabilities
Debt Instrument [Line Items]
Contingent obligation – principal	(12.9)	(12.9)
Contingent obligation – accrued interest	(18.0)	(16.6)
Contingent obligation – derivative asset	$ 30.9	$ 29.5
Long-term Debt | E.ON Contingent Obligation
Debt Instrument [Line Items]
Number of monthly installments | paymentInstallment	72
Stated interest rate	10.94%
Realized gain (loss) on contingent obligation	$ 1.4

X

- Definition

Sum of the carrying values as of the balance sheet date of the E.ON Contingent Obligation which is debt initially having maturities due after one year from the balance sheet date or beyond the operating cycle, if longer, but excluding the portions thereof scheduled to be repaid within one year or the normal operating cycle, if longer. The E.ON contingent obligation consists of the aggregate E.ON payments. Obligation to make repayments is contingent upon certain operating criteria. When the conditions for repayment are met, and for so long so those conditions continue to be met, there is obligation to make principal and interest payments.

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This amount represents the accrued interest on the E.ON contingent obligation, which is defined as the sum of the carrying values as of the balance sheet date of the E.ON Contingent Obligation which is debt initially having maturities due after one year from the balance sheet date or beyond the operating cycle, if longer, but excluding the portions thereof scheduled to be repaid within one year or the normal operating cycle, if longer. The E.ON contingent obligation consists of the aggregate E.ON payments. Obligation to make repayments is contingent upon certain operating criteria. When the conditions for repayment are met, and for so long so those conditions continue to be met, there is obligation to make principal and interest payments.

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This amount represents the derivative asset recorded for the E.ON contingent obligation, which is defined as the sum of the carrying values as of the balance sheet date of the E.ON Contingent Obligation which is debt initially having maturities due after one year from the balance sheet date or beyond the operating cycle, if longer, but excluding the portions thereof scheduled to be repaid within one year or the normal operating cycle, if longer. The E.ON contingent obligation consists of the aggregate E.ON payments. Obligation to make repayments is contingent upon certain operating criteria. When the conditions for repayment are met, and for so long so those conditions continue to be met, there is obligation to make principal and interest payments.

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This amount represents the principal amount of the E.ON contingent obligation, which is defined as the sum of the carrying values as of the balance sheet date of the E.ON Contingent Obligation which is debt initially having maturities due after one year from the balance sheet date or beyond the operating cycle, if longer, but excluding the portions thereof scheduled to be repaid within one year or the normal operating cycle, if longer. The E.ON contingent obligation consists of the aggregate E.ON payments. Obligation to make repayments is contingent upon certain operating criteria. When the conditions for repayment are met, and for so long so those conditions continue to be met, there is obligation to make principal and interest payments.

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The net change in the difference between the fair value and the carrying value on the contingent obligation held at each balance sheet date, that was included in earnings for the period.

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