Financial Instruments and Other Guarantees (Details) - USD ($) $ in Millions	Sep. 30, 2023	Apr. 14, 2023	Mar. 31, 2023	Dec. 31, 2022
Guarantee Obligations [Line Items]
Restricted Cash	$ 643.1			$ 110.3
Deposits Assets	223.0			77.1
Restricted cash and collateral	866.1			187.4
LC Facility
Guarantee Obligations [Line Items]
Deposits Assets	0.0			28.5
Surety Trust Account
Guarantee Obligations [Line Items]
Restricted Cash	471.1		$ 566.3	0.0
Collateralized letters of credit funding
Guarantee Obligations [Line Items]
Restricted Cash	172.0			110.3
Deposits with Regulatory Authorities
Guarantee Obligations [Line Items]
Deposits Assets	223.0			33.6
Deposits Held on Behalf of Surety
Guarantee Obligations [Line Items]
Deposits Assets	0.0			15.0
Asset Retirement Obligations
Guarantee Obligations [Line Items]
Letters of credit outstanding, amount	6.0			437.8
Surety Bonds and Letters of Credit Outstanding for Reclamation Support	1,076.0			1,687.9
Letters of Credit in Support of Surety Bonds	(6.0)			(431.7)
Total Obligations Supported, Net	1,070.0			1,256.2
Surety bonds amount	1,070.0			1,250.1
Asset Retirement and Other Obligations
Guarantee Obligations [Line Items]
Letters of credit outstanding, amount	107.4			569.6
Total Surety Bonds and Letters of Credit Outstanding	1,305.3			1,946.4
Total Letters of Credit in Support of Surety Bonds	(17.5)			(468.9)
Total Obligations Supported, Net	1,287.8			1,477.5
Surety bonds amount	1,197.9			1,376.8
Other Obligations
Guarantee Obligations [Line Items]
Letters of credit outstanding, amount	101.4			131.8
Surety Bonds and Letters of Credit Outstanding for Other Support	229.3			258.5
Letters of Credit in Support of Surety Bonds	(11.5)			(37.2)
Total Obligations Supported, Net	217.8			221.3
Surety bonds amount	$ 127.9			$ 126.7
LC Facility
Guarantee Obligations [Line Items]
Mandatory Repurchase, Percentage of Accreted Value	95.00%
Debt instrument, repurchase amount	$ 30.0	$ 30.0
Secured debt | Accounts Receivable Securitization Program
Guarantee Obligations [Line Items]
Letters of credit outstanding, amount	107.4
Collateralized Letter of Credit Agreement
Guarantee Obligations [Line Items]
Letters of credit outstanding, amount	$ 167.0