CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Revenues	$ 1,990.2	$ 1,886.4	$ 3,793.6	$ 3,472.7
Cost of sales	1,632.3	1,550.4	3,107.4	2,893.7
Gross income	357.9	336.0	686.2	579.0
Operating expenses:
Selling, general and administrative	173.0	170.4	331.6	328.3
Amortization of purchased intangibles	9.3	9.2	18.5	19.8
Total operating expenses	182.3	179.6	350.1	348.1
Operating income	175.6	156.4	336.1	230.9
Other income (expense):
Interest expense	(13.7)	(16.1)	(27.4)	(31.5)
Interest income	2.0	8.1	4.2	9.8
Miscellaneous, net	1.2	(1.3)	0.0	(1.5)
Income before income taxes and earnings (losses) of unconsolidated affiliates	165.1	147.1	312.9	207.7
Provision for income taxes	36.2	36.2	75.9	40.9
Income before earnings (losses) of unconsolidated affiliates	128.9	110.9	237.0	166.8
Equity in earnings (losses) of unconsolidated affiliates	(0.4)	(0.1)	0.5	0.4
Net income	$ 128.5	$ 110.8	$ 237.5	$ 167.2
Earnings per share:
Basic earnings per share (in dollars per share)	$ 1.84	$ 1.49	$ 3.37	$ 2.24
Diluted earnings per share (in dollars per share)	1.82	1.47	3.33	2.21
Cash dividends declared per share on common stock (in dollars per share)	$ 0.27	$ 0.24	$ 0.54	$ 0.48