Consolidated Statements of Cash Flows $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Operating activities
Net income	$ 530.1	$ 617.0	$ 354.9
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation expense	251.6	230.6	214.1
Amortization expense	0.1	0.4	0.2
Amortization of deferred financing fees	3.5	17.9	3.4
Accretion of customer supply agreement	4.3	4.1	2.6
Employee stock compensation expense	36.1	27.4	22.1
Loss (gain) from derivative instruments	8.1	(7.2)	(0.9)
Loss (gain) from foreign currency transactions	1.6	(0.3)	(8.1)
Loss on impairment and disposition of assets	4.9	1.8	9.5
Deferred taxes	86.1	(38.0)	52.4
Pension and other post-retirement benefits, net	(20.0)	(33.4)	(34.7)
Grant liability amortization	(16.2)	(21.6)	(19.0)
Equity in net income of affiliates	0.2	(0.6)	(0.3)
Increase (Decrease) in Forward Position	40.7	(170.9)	0.0
Changes in assets and liabilities
Accounts receivable, net	12.8	(47.9)	(48.5)
Inventory, net	(95.4)	(61.3)	319.6
Increase (Decrease) in Contract with Customer, Asset	(5.2)	(8.5)
Accounts payable and accrued liabilities	34.6	244.5	160.3
Profit sharing/deferred compensation	16.0	(40.9)	7.6
Advance payments	120.8	(98.3)	(209.6)
Income taxes receivable/payable	(59.6)	(28.4)	25.7
Increase (Decrease) in Contract with Customer, Liability	(13.0)	208.3
Deferred revenue and other deferred credits	6.2	16.9	(231.2)
Other	(25.6)	(41.7)	(46.4)
Net cash provided by operating activities	922.7	769.9	573.7
Investing activities
Purchase of property, plant and equipment	(232.2)	(271.2)	(273.1)
Proceeds from sale of assets	0.2	3.4	0.4
Payments to Acquire Interest in Subsidiaries and Affiliates	(7.9)
Other Investing Activities	7.7	0.0	0.1
Payments for (Proceeds from) Other Investing Activities	0.0	0.0	0.1
Net cash used in investing activities	(239.9)	(267.8)	(272.8)
Financing activities
Proceeds from Issuance of Senior Long-term Debt	250.0	1,300.0	0.0
Proceeds from revolving credit facility	900.0	0.0	0.0
Payments on revolving credit facility	100.0	0.0	0.0
Principal payments of debt	13.4	6.7	2.8
Repayments of Debt	(16.6)	(256.3)	(25.0)
Early Repayment of Senior Debt	0.0	300.0	0.0
Payment, Tax Withholding, Share-based Payment Arrangement	(12.9)	(15.6)	(14.2)
Proceeds from Stock Plans	2.6	2.1	0.0
Debt issuance and financing costs	0.0	23.2	0.9
Proceeds from Other Debt	0.0	0.0	7.6
Payments for Repurchase of Common Stock	(75.8)	(805.8)	(496.3)
Payments of Dividends	(50.4)	(48.0)	(47.1)
Proceeds from (Payments for) Other Financing Activities	0.9
Net cash provided by (used in) financing activities	884.4	(153.5)	(578.7)
Effect of exchange rate changes on cash and cash equivalents	5.9	0.0	5.6
Net increase (decrease) in cash, cash equivalents, and restricted cash for the period	1,573.1	348.6	(272.2)
Cash, cash equivalents, and restricted cash, end of period	2,350.5	773.6	423.3
Restricted Cash, Current	0.3	0.3	2.2
Restricted Cash and Investments, Noncurrent	16.4	20.2	20.0
Supplemental information
Interest paid	93.2	70.4	43.6
Income taxes paid	105.0	202.3	101.9
Property acquired through capital leases	120.3	26.8	29.3
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 2,367.2	$ 794.1	$ 445.5