STATEMENTS OF CONSOLIDATED CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net (loss) income	$ (18.5)	$ 28.8	$ 62.0
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Depreciation of property, plant and equipment	82.5	49.3	46.3
Amortization of definite-lived intangible assets	9.0	2.9	2.8
Amortization of debt premium and debt issuance costs	2.1	2.0	1.2
Deferred income taxes	(11.4)	15.2	21.1
Non-cash equity compensation	12.9	10.0	9.8
Non-cash asset impairment charges		0.5	26.1
Loss on extinguishment of debt	35.9		20.3
(Gain) loss on disposition of property, plant and equipment	(0.5)	0.2
Loss (gain) on disposition of short-term investments		(0.7)	(0.9)
Non-cash defined benefit net periodic postretirement benefit cost	9.4	5.2	7.0
Changes in operating assets and liabilities, net of effects of acquisition:
Trade and other receivables	(90.3)	60.8	20.2
Contract assets	(27.1)	18.5	0.3
Inventories	(43.5)	25.6	37.5
Prepaid expenses and other current assets	(0.9)	(6.8)	4.2
Accounts payable	112.5	(5.9)	(24.5)
Accrued liabilities	17.3	(0.6)	(5.0)
Annual variable cash contributions to Salaried VEBA	(1.7)	(2.9)	(2.1)
Long-term assets and liabilities, net	(8.3)	4.8	6.0
Net cash provided by operating activities	79.4	206.9	232.3
Cash flows from investing activities:
Capital expenditures	(58.0)	(51.9)	(60.2)
Purchase of short-term investments		(39.1)	(132.2)
Purchase of equity securities	(0.4)	(0.5)	(0.7)
Proceeds from disposition of short-term investments		118.1	91.1
Cash payment for acquisition of Warrick, net of cash received – Note 4	(609.2)
Proceeds from disposal of property, plant and equipment	1.8	0.3	0.2
Net cash (used in) provided by investing activities	(665.8)	26.9	(101.8)
Cash flows from financing activities:
Cash paid for debt issuance costs	(8.6)	(6.2)	(8.8)
Repayment of finance lease	(2.1)	(1.7)	(1.4)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares	(2.6)	(4.3)	(6.2)
Repurchase of common stock		(12.5)	(44.2)
Cash dividends and dividend equivalents paid	(46.7)	(43.4)	(39.4)
Net cash provided by financing activities	109.1	281.9	8.5
Net (decrease) increase in cash, cash equivalents and restricted cash during the period	(477.3)	515.7	139.0
Cash, cash equivalents and restricted cash at beginning of period	794.3	278.6	139.6
Cash, cash equivalents and restricted cash at end of period	317.0	794.3	278.6
6.50% Senior Notes
Cash flows from financing activities:
Repayment of principal and redemption premium of Senior Notes	(380.9)
Issuance of Senior Notes		$ 350.0
5.875% Senior Notes
Cash flows from financing activities:
Repayment of principal and redemption premium of Senior Notes			(391.5)
4.50% Senior Notes
Cash flows from financing activities:
Issuance of Senior Notes	$ 550.0
4.625% Senior Notes
Cash flows from financing activities:
Issuance of Senior Notes			$ 500.0