STATEMENTS OF CONSOLIDATED CASH FLOWS (UNAUDITED) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net (loss) income		$ 22.5	$ 47.2
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property, plant and equipment		24.8	22.6
Amortization of definite-lived intangible assets		1.4	1.4
Amortization of debt premium and debt issuance costs		0.8	0.6
Deferred income taxes		15.8	18.3
Non-cash equity compensation		4.7	6.1
Gain on disposition of short-term investments		(0.7)	(0.4)
Non-cash asset impairment charge		0.0	0.1
Loss (gain) on disposition of property, plant and equipment		0.3	(0.2)
Other non-cash changes in assets and liabilities		3.1	6.1
Changes in operating assets and liabilities:
Trade and other receivables		36.5	2.2
Contract assets		13.0	8.0
Inventories		(3.8)	(16.0)
Prepaid expenses and other current assets		(7.6)	(4.3)
Accounts payable		(28.7)	(13.4)
Accrued liabilities		10.9	(6.6)
Annual variable cash contributions to Salaried VEBA		(2.9)	(2.1)
Long-term assets and liabilities, net		4.8	0.9
Net cash provided by operating activities	[1]	94.9	70.5
Cash flows from investing activities:
Capital expenditures		(31.8)	(29.9)
Purchase of short-term investments		(39.1)	(33.0)
Purchase of equity securities		(0.5)	(0.7)
Proceeds from disposition of short-term investments		118.1	45.7
Proceeds from disposition of property, plant and equipment		0.0	0.2
Net cash provided by (used in ) investing activities	[1]	46.7	(17.7)
Cash flows from financing activities:
Issuance of 6.50% Senior Notes		350.0	0.0
Cash paid for debt issuance costs		(6.1)	0.0
Repayment of finance lease		(0.8)	(0.6)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		(4.3)	(6.2)
Repurchase of common stock		(12.5)	(28.6)
Cash dividends and dividend equivalents paid		(21.9)	(20.1)
Net cash provided by (used in) financing activities		304.4	(55.5)
Net increase (decrease) in cash, cash equivalents and restricted cash during the period		446.0	(2.7)
Cash, cash equivalents and restricted cash at beginning of period		278.6	139.6
Cash, cash equivalents and restricted cash at end of period		$ 724.6	$ 136.9

[1] See Note 13 for supplemental cash flow information.