Acquisition of Jamalco - Fair Value of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Millions	May 02, 2023	Sep. 30, 2023	Dec. 31, 2022
Less: identifiable assets acquired and liabilities assumed
Deferred credit - preliminary bargain purchase gain		$ (161.6)	$ 0.0
General Alumina Holdings Limited
Consideration transferred
Cash paid	$ 8.3
Total consideration transferred	8.3
Less: identifiable assets acquired and liabilities assumed
Cash and cash equivalents	19.4
Restricted cash	8.3
Inventories	93.4
Accounts receivable - net	8.0
Prepaid and other current assets	7.8
Property, plant and equipment - net	250.9
Other assets	28.0
Accounts payable, trade	(92.9)
Accrued and other current liabilities	(33.9)
Other liabilities	(24.5)
Asset retirement obligations	(36.5)
Total identifiable net assets acquired	228.0
Less: noncontrolling interest	(58.1)
Deferred credit - preliminary bargain purchase gain	(161.6)
Fair value allocated to net assets acquired, net of bargain purchase gain	$ 8.3