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Commitments and Contingencies (Details) - USD ($) $ in Millions		1 Months Ended			3 Months Ended
	Jan. 31, 2020	Dec. 31, 2019	Apr. 30, 2019	Mar. 31, 2019	Jun. 30, 2021	Dec. 06, 2019	Dec. 31, 2014
New York
Commitments and Contingencies
Contingency liability					$ 146.0
Percentage of claim recoveries due to seller	90.00%
Percentage of claim recoveries due to purchaser	10.00%
Montana
Commitments and Contingencies
Damages sought			$ 132.0	$ 79.0
Damages sought, counter party		$ 93.0
Department of Energy | New York | Minimum
Commitments and Contingencies
Contingency liability					106.0
Department of Energy | New York | Maximum
Commitments and Contingencies
Contingency liability					146.0
Fund investment capital commitments
Commitments and Contingencies
Commitment					$ 20.3
Commitment period					8 years
Standby letters of credit
Commitments and Contingencies
Contingency liability					$ 500.2
Surety Bond
Commitments and Contingencies
Contingency liability					3,800.0
Collectibility of Receivables
Commitments and Contingencies
Unapproved change orders							$ 103.0
Collectibility of Receivables | New York
Commitments and Contingencies
Unapproved change orders						$ 60.4
Collectibility of Receivables | New York | Minimum
Commitments and Contingencies
Damages sought					148.5
Collectibility of Receivables | New York | Maximum
Commitments and Contingencies
Damages sought					329.4
Collectibility of Receivables | Montana
Commitments and Contingencies
Unapproved change orders					90.0
Damages sought					$ 144.0

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The value of the award the counter party seeks in the legal matter.

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Percentage of claim recoveries and costs due to purchaser.

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Percentage of claim recoveries and costs due to seller.

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The minimum amount the entity agreed to spend under the long-term purchase commitment.

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Period covered by the long-term purchase commitment, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The value (monetary amount) of the award the plaintiff seeks in the legal matter.

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Amount of cost incurred on construction contract for unapproved change order, claim, or similar item subject to uncertainty.

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