STATEMENTS OF CONSOLIDATED CASH FLOWS (UNAUDITED) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net income		$ 22.9	$ 72.6
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property, plant and equipment		37.0	34.2
Amortization of definite-lived intangible assets		2.1	2.1
Amortization of debt premium and debt issuance costs		1.4	0.9
Deferred income taxes		14.8	27.8
Non-cash equity compensation		7.4	8.4
Gain on disposition of short-term investments		(0.7)	(0.6)
Non-cash asset impairment charge		0.5	0.1
Loss (gain) on disposition of property, plant and equipment		0.1	(0.1)
Other non-cash changes in assets and liabilities		2.0	9.3
Changes in operating assets and liabilities:
Trade and other receivables		43.4	(8.8)
Contract assets		19.8	8.8
Inventories		20.1	22.6
Prepaid expenses and other current assets		(4.6)	(1.7)
Accounts payable		(27.6)	(21.9)
Accrued liabilities		5.4	(3.3)
Annual variable cash contributions to Salaried VEBA		(2.9)	(2.1)
Long-term assets and liabilities, net		9.6	5.6
Net cash provided by operating activities	[1]	150.7	153.9
Cash flows from investing activities:
Capital expenditures		(37.2)	(40.7)
Purchase of short-term investments		(39.1)	(56.3)
Purchase of equity securities		(0.5)	(0.7)
Proceeds from disposition of short-term investments		118.1	68.2
Proceeds from disposition of property, plant and equipment		0.3	0.2
Net cash provided by (used in) investing activities	[1]	41.6	(29.3)
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		(1.2)	(1.1)
Cancellation of shares to cover employees' tax withholdings upon vesting of non-vested shares		(4.3)	(6.2)
Repurchase of common stock		(12.5)	(40.6)
Cash dividends and dividend equivalents paid		(32.7)	(29.8)
Net cash provided by (used in) financing activities	[1]	293.2	(77.7)
Net increase in cash, cash equivalents and restricted cash during the period		485.5	46.9
Cash, cash equivalents and restricted cash at beginning of period		278.6	139.6
Cash, cash equivalents and restricted cash at end of period		$ 764.1	$ 186.5

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