Revenue Recognition (Balance Sheet Impact Upon Adoption) (Details) - USD ($) $ in Millions	Jun. 30, 2019	Mar. 31, 2019	Oct. 01, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017
Assets
Cash and cash items	$ 2,696.8		$ 2,791.3	$ 2,791.3
Short-term investments	0.0		184.7	184.7
Trade receivables, net	1,340.7		1,207.2	1,207.2
Inventories	408.3		396.1	396.1
Contracts in progress, less progress billings			0.0	77.5
Prepaid expenses	97.2		129.6	129.6
Other receivables and current assets			399.5	295.8
Total Current Assets	4,915.2		5,108.4	5,082.2
Total Noncurrent Assets	14,616.7		14,096.1	14,096.1
Total Assets	19,531.9		19,204.5	19,178.3
Liabilities and Equity
Payables and accrued liabilities	1,543.2		1,844.0	1,817.8
Accrued income taxes	65.6		59.6	59.6
Short-term borrowings	79.9		54.3	54.3
Current portion of long-term debt	466.5		406.6	406.6
Total Current Liabilities	2,155.2		2,364.5	2,338.3
Total Noncurrent Liabilities	5,650.1		5,663.7	5,663.7
Total Liabilities	7,805.3		8,028.2	8,002.0
Total Equity	11,726.6	$ 11,503.4	11,176.3	11,176.3	$ 10,810.0	$ 10,693.2	$ 10,185.5
Total Liabilities and Equity	$ 19,531.9		19,204.5	$ 19,178.3
ASU Update 2014-09 | New Revenue Standard Adjustments
Assets
Cash and cash items			0.0
Short-term investments			0.0
Trade receivables, net			0.0
Inventories			0.0
Contracts in progress, less progress billings			(77.5)
Prepaid expenses			0.0
Other receivables and current assets			103.7
Total Current Assets			26.2
Total Noncurrent Assets			0.0
Total Assets			26.2
Liabilities and Equity
Payables and accrued liabilities			26.2
Accrued income taxes			0.0
Short-term borrowings			0.0
Current portion of long-term debt			0.0
Total Current Liabilities			26.2
Total Noncurrent Liabilities			0.0
Total Liabilities			26.2
Total Equity			0.0
Total Liabilities and Equity			$ 26.2