Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net earnings (loss)	$ 35.4	$ (226.2)
Adjustments to reconcile net earnings (loss) to net cash provided by operating activities:
Depreciation and amortization	25.6	18.2
Deferred income taxes	1.2	(93.0)
Share-based compensation	2.3	0.9
Loss on disposal of discontinued operations	0.4	5.0
Equity earnings from joint venture	(21.0)	(19.5)
U.S. pension cost		371.6
Other non-cash adjustments, net	0.2	0.2
Changes in operating assets and liabilities:
Receivables	(12.9)	(12.5)
Inventories	(2.1)	(1.0)
Accounts payable and accrued expenses	(9.2)	(25.8)
Income taxes receivable and payable, net	5.5	13.0
Other assets and liabilities	(5.8)	(5.2)
Net cash provided by operating activities	19.6	25.7
Cash flows from investing activities:
Purchases of property, plant and equipment	(13.2)	(12.0)
Return of investment from joint venture	16.5	18.1
Payments to Knauf upon disposal of discontinued operations	(11.8)
Other investing activities	(0.3)	3.8
Net cash (used for) provided by investing activities	(8.8)	9.9
Cash flows from financing activities:
Proceeds from short-term debt		30.0
Payments for finance leases	(0.5)
Proceeds from revolving credit facility	50.0	100.0
Payments of revolving credit facility	(50.0)	(20.0)
Payments of long-term debt	(6.3)
Dividends paid	(10.1)	(9.6)
Proceeds from share-based compensation plans, net of tax	0.7	0.8
Payments for treasury stock acquired	(10.0)	(34.4)
Net cash (used for) provided by financing activities	(26.2)	66.8
Effect of exchange rate changes on cash and cash equivalents	0.1	(0.8)
Net (decrease) increase in cash and cash equivalents	(15.3)	101.6
Cash and cash equivalents at beginning of year	136.9	45.3
Cash and cash equivalents at end of period	121.6	146.9
Supplemental Cash Flow Disclosures:
Interest paid	5.7	6.9
Income tax payments, net	7.2	1.1
Amounts in accounts payable for capital expenditures	$ 0.7	$ 0.1