New Accounting Guidance (Balance Sheet Impacts) (Details) - USD ($) $ in Millions	Oct. 01, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash and cash items	$ 2,791.3	$ 2,791.3	$ 3,273.6	$ 1,293.2
Short-term investments	184.7	184.7	404.0
Trade receivables, net	1,207.2	1,207.2	1,174.0
Inventories	396.1	396.1	335.4
Contracts in progress, less progress billings	0.0	77.5	84.8
Prepaid expenses	129.6	129.6	191.4
Other receivables and current assets	399.5	295.8	403.3
Total Current Assets	5,108.4	5,082.2	5,876.7
Total Noncurrent Assets	14,096.1	14,096.1	12,590.5
Total Assets	19,204.5	19,178.3	18,467.2	18,028.6
Payables and accrued liabilities	1,844.0	1,817.8	1,814.3
Accrued income taxes	59.6	59.6	98.6
Short-term borrowings	54.3	54.3	144.0
Current portion of long-term debt	406.6	406.6	416.4
Total Current Liabilities	2,364.5	2,338.3	2,489.0
Total Noncurrent Liabilities	5,663.7	5,663.7	5,792.7
Total Liabilities	8,028.2	8,002.0	8,281.7
Total Equity	11,176.3	11,176.3	10,185.5	$ 7,213.4	$ 7,381.1
Total Liabilities and Equity	19,204.5	$ 19,178.3	$ 18,467.2
Estimated Impact Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
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
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