Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 2,188.0	$ 2,072.7	$ 1,981.5
Operating costs and expenses:
Cost of sales (exclusive of items shown separately below)	1,800.1	1,701.3	1,613.6
Selling, general and administrative expense	46.0	56.1	53.6
Depreciation and amortization	61.4	65.3	74.5
Other expense, net	23.5	9.4	1.6
Total operating costs and expenses	1,931.0	1,832.1	1,743.3
Operating income	257.0	240.6	238.2
Non-operating:
Retirement benefits expense	33.9	36.6	26.1
Loss on debt	10.5	0.0	0.0
Interest income	(2.5)	(6.3)	(15.5)
Interest expense	20.1	30.1	35.7
Total non-operating expense, net	62.0	60.4	46.3
Income before income taxes	195.0	180.2	191.9
Income tax provision	51.3	42.5	50.9
Net income	$ 143.7	$ 137.7	$ 141.0
Earnings per share of common stock
Basic earnings per share (in USD per share)	$ 1.80	$ 1.76	$ 1.79
Diluted earnings per share (in USD per share)	$ 1.75	$ 1.66	$ 1.69
Weighted average shares of common stock outstanding, basic (in shares)	79.2	77.4	77.2
Weighted average shares of common stock outstanding, diluted (in shares)	81.7	81.9	81.7
Cash dividends paid per share (in USD per share)	$ 5.00	$ 0	$ 0