Other Balance Sheet Accounts (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Schedule of other assets and other liabilities [Line Items]
Current asset, related party	$ 191.3	$ 173.9
Nontrade Receivables, Current	21.0	24.1
Derivative Asset, Current	4.8	15.6
Income Taxes Receivable	4.6	4.2
Other Assets, Miscellaneous, Current	14.4	17.3
Other current assets	236.1	235.1
Other Current Liabilities
Current liability, related party	191.3	173.9
Employee-related Liabilities, Current	46.2	53.6
Deferred revenue (see Note 13)	33.5	35.0
Environmental contingencies (see Note 8)	20.2	17.8
Pension liabilities (see Note 6)	14.9	14.8
Accrued interest (see Note 3)	13.8	13.3
Income taxes payable (see Note 5)	10.9	8.6
Operating Lease, Liability, Current	9.0	9.3
Liability for dam spillway replacement, current	8.8	4.7
Other accrued liabilities	80.1	88.7
Total Other Current Liabilities	428.7	419.7
Other Liabilities, Noncurrent
Environmental contingencies (see Note 8)	91.6	97.5
Liability for dam spillway replacement	54.0	61.7
Deferred revenue (see Note 13)	24.5	29.5
Operating Lease, Liability, Noncurrent	25.1	26.2
Legacy Product Liability	24.0	24.0
Retained obligations of divested businesses	12.1	12.7
Asset retirement obligation	9.6	9.4
Deferred Income Tax Liabilities, Net	7.9	7.5
Derivative Liability, Noncurrent	5.6	13.2
Unrecognized Tax Benefits, Net of Deferred Taxes	4.1	4.1
Other noncurrent liabilities	22.7	22.4
Other Liabilities, Noncurrent	$ 281.2	$ 308.2