New Accounting Standards - Schedule of Effect of New Revenue Recognition Guidance to Condensed Consolidated Financial Statements (Details) - USD ($) $ in Millions	Jun. 30, 2019	Oct. 01, 2018	Sep. 30, 2018
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Receivables, net	$ 1,263.9		$ 1,286.2
Unbilled receivables, net	501.1		235.4
Inventories, net	1,361.4		1,227.7
Other current assets	82.6		66.0
Total current assets	3,361.2		3,269.9
Other long-term assets	124.4		65.9
Total assets	5,446.4		5,294.2
Customer advances	434.6	$ 472.1	444.9
Other current liabilities	333.8		275.8
Total current liabilities	1,687.5		1,690.1
Other long-term liabilities	343.3		272.6
Retained earnings	2,373.4		2,007.9
Total shareholders’ equity	2,596.9		2,513.5
Total liabilities and shareholders’ equity	5,446.4		$ 5,294.2
Accounting Standards Update 2014-09
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Receivables, net		1,272.7
Unbilled receivables, net		309.7
Inventories, net		1,151.8
Other current assets		66.3
Total current assets		3,255.1
Other long-term assets		84.6
Total assets		5,298.1
Customer advances		472.1
Other current liabilities		282.2
Total current liabilities		1,723.7
Other long-term liabilities		303.3
Retained earnings		1,947.5
Total shareholders’ equity		2,453.1
Total liabilities and shareholders’ equity		5,298.1
Accounting Standards Update 2014-09 | Impact of New Revenue Recognition Standard [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Receivables, net	(7.2)	(13.5)
Unbilled receivables, net	98.0	74.3
Inventories, net	(90.8)	(75.9)
Other current assets	(0.1)	0.3
Total current assets	(0.1)	(14.8)
Other long-term assets	14.3	18.7
Total assets	14.2	3.9
Customer advances	(3.1)	27.2
Other current liabilities	21.9	6.4
Total current liabilities	18.8	33.6
Other long-term liabilities	40.4	30.7
Retained earnings	(45.0)	(60.4)
Total shareholders’ equity	(45.0)	(60.4)
Total liabilities and shareholders’ equity	14.2	$ 3.9
Accounting Standards Update 2014-09 | Previous Accounting Guidance [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Receivables, net	1,271.1
Unbilled receivables, net	403.1
Inventories, net	1,452.2
Other current assets	82.7
Total current assets	3,361.3
Other long-term assets	110.1
Total assets	5,432.2
Customer advances	437.7
Other current liabilities	311.9
Total current liabilities	1,668.7
Other long-term liabilities	302.9
Retained earnings	2,418.4
Total shareholders’ equity	2,641.9
Total liabilities and shareholders’ equity	$ 5,432.2