Commitments and Contingent Liabilities (Details) $ in Millions	3 Months Ended			12 Months Ended			36 Months Ended	71 Months Ended
	Sep. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Feb. 03, 2017 USD ($)	Dec. 31, 2019 USD ($) shares
Environmental remediation
ZAI PD Account Funding							$ 49.4
ZAI P D Account, Maximum Number of Contingent Deferred Payments				10
ZAI P D Account, Deferred Payments, Each Year for Twenty Years				$ 8.0
Period in Which ZAI PD Contingent Deferred Payments Will be Made				20 years
Minimum ZAI P D Account Assets for Condition in Relation to Contingent Obligation Payments				$ 10.0				$ 10.0
Document Period End Date				Dec. 31, 2019
ZAI PD Claims paid by the Trust								29.0
ZAI PD Trust Balance				$ 23.0				23.0
ZAI PD Attorney's fees paid by the Trust								$ 15.0
Frequency of PD Trust Payments				6 months
Estimated annual expenses related to PD Trust				$ 0.2
Number of Shares Issuable under Warrant | shares				77,372,257				77,372,257
Estimated liability for environmental investigative and remediation costs				$ 115.3	$ 126.4			$ 115.3
Pre-tax charges for environmental matters				1.7	73.8	$ 24.4
Legacy Product Charge				$ 24.0
Remaining Period in Which ZAI PD Contingent Deferred Payments May be Made				19 years
Total Maximum Financial Obligation for ZAI PD Account Contingent Deferred Payments				$ 80.0
Maximum Annual Obligation for ZAI PD Account Contingent Deferred Payments				8.0
Vermiculite Related Matters [Member]
Environmental remediation
Estimated liability for environmental investigative and remediation costs				76.0	81.7			76.0
Pre-tax charges for environmental matters				0.0	70.2	9.5
Operable Unit 3 [Member]
Environmental remediation
Pre-tax charges for environmental matters	$ 70.0		$ 70.0
Non Vermiculite Related Matters [Member]
Environmental remediation
Estimated liability for environmental investigative and remediation costs				39.3	44.7			39.3
Pre-tax charges for environmental matters				1.7	$ 3.6	14.9
Accrual for Environmental Loss Contingencies, Charges to Expense for New Losses						$ 7.2
Environmental Exit Costs, Nature of Costs						P10Y
Minimum | Operable Unit 3 [Member]
Environmental remediation
Loss Contingency, Estimate of Possible Loss				30.0				30.0
Minimum | Spillway [Member]
Environmental remediation
Loss Contingency, Estimate of Possible Loss				50.0				50.0
Maximum | Operable Unit 3 [Member]
Environmental remediation
Loss Contingency, Estimate of Possible Loss				170.0				170.0
Maximum | Spillway [Member]
Environmental remediation
Loss Contingency, Estimate of Possible Loss				100.0				100.0
ZAI PD Trust [Member] | Minimum
Environmental remediation
Loss Contingency, Estimate of Possible Loss				16.0				16.0
ZAI PD Trust [Member] | Maximum
Environmental remediation
Loss Contingency, Estimate of Possible Loss				24.0				$ 24.0
Spillway [Member]
Environmental remediation
Loss Contingency, Loss in Period		$ 45.0		$ 68.0
Spillway [Member] | Minimum
Environmental remediation
Site Contingency, Time Frame of Disbursements				P3Y
Spillway [Member] | Maximum
Environmental remediation
Site Contingency, Time Frame of Disbursements				P4Y