Consolidated Statements of Income and Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Net sales	$ 1,807.2	$ 1,708.7
Cost of sales	(1,403.5)	(1,343.7)
Gross profit	403.7	365.0
Selling, general and administrative expenses	(145.0)	(145.9)
Other expense, net	(20.4)	(10.0)
Income from operations	238.3	209.1
Non-operating pension income	4.8	0.6
Interest expense, net	(23.5)	(19.6)
Income before taxes	219.6	190.1
Provision for income taxes	(53.1)	(48.4)
Net income	$ 166.5	$ 141.7
Net income per common share:
Basic	$ 1.75	$ 1.50
Diluted	1.75	1.49
Dividends declared per common share	$ 1.00	$ 0.79
Statements of Comprehensive Income:
Net income	$ 166.5	$ 141.7
Changes in unrealized losses on marketable debt securities, net of tax of $0.0 million and $0.1 million, for 2021 and 2020, respectively	(0.1)	(0.2)
Amortization of pension and postretirement plans actuarial loss and prior service cost, net of tax of $0.8 million and $0.9 million, for 2021 and 2020, respectively	2.5	2.7
Other comprehensive income	2.4	2.5
Comprehensive income	$ 168.9	$ 144.2