Debt (Long-term Debt) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Debt Instrument [Line Items]
Long-term Debt, gross	$ 3,837.3	$ 4,298.5
Less: Unamortized Discount and Debt Issuance Costs	(18.5)	(23.4)
Total Long-term Debt	3,818.8	4,275.1
Less: Current portion of long-term debt	(416.4)	(365.4)
Long-term Debt	3,402.4	3,909.7
Debentures | Debenture 8.75% due 2021
Debt Instrument [Line Items]
Long-term Debt, gross	$ 18.4	18.4
Interest rate, stated percentage	8.75%
Medium-term Notes | Series E 7.6% due 2026
Debt Instrument [Line Items]
Long-term Debt, gross	$ 17.2	17.2
Interest rate, weighted average	7.60%
Senior Notes | Note 1.2% due 2018
Debt Instrument [Line Items]
Long-term Debt, gross	$ 400.0	400.0
Interest rate, stated percentage	1.20%
Senior Notes | Note 4.375% due 2019
Debt Instrument [Line Items]
Long-term Debt, gross	$ 400.0	400.0
Interest rate, stated percentage	4.375%
Senior Notes | Note 3.0% due 2022
Debt Instrument [Line Items]
Long-term Debt, gross	$ 400.0	400.0
Interest rate, stated percentage	3.00%
Senior Notes | Note 2.75% due 2023
Debt Instrument [Line Items]
Long-term Debt, gross	$ 400.0	400.0
Interest rate, stated percentage	2.75%
Senior Notes | Note 3.35% due 2024
Debt Instrument [Line Items]
Long-term Debt, gross	$ 400.0	400.0
Interest rate, stated percentage	3.35%
Bonds | Variable-rate industrial revenue bonds .87% due 2035 to 2050
Debt Instrument [Line Items]
Long-term Debt, gross	$ 631.9	769.9
Interest rate, weighted average	0.87%
Bonds | Other .89% due 2018 to 2019
Debt Instrument [Line Items]
Long-term Debt, gross	$ 10.9	25.7
Interest rate, weighted average	0.89%
Bonds | Eurobonds 4.625% due 2017
Debt Instrument [Line Items]
Long-term Debt, gross	$ 0.0	337.0
Interest rate, stated percentage	4.625%
Bonds | Eurobonds 2.0% due 2020
Debt Instrument [Line Items]
Long-term Debt, gross	$ 354.4	337.0
Interest rate, stated percentage	2.00%
Bonds | Eurobonds 1.0% due 2025
Debt Instrument [Line Items]
Long-term Debt, gross	$ 354.4	337.0
Interest rate, stated percentage	1.00%
Bonds | Eurobonds .375% due 2021
Debt Instrument [Line Items]
Long-term Debt, gross	$ 413.5	393.2
Interest rate, stated percentage	0.375%
Bonds | Other Foreign 4.3% due 2018 to 2022
Debt Instrument [Line Items]
Long-term Debt, gross	$ 25.8	52.9
Interest rate, stated percentage	4.30%
Capital Lease Obligations | United States 5.0% due 2018
Debt Instrument [Line Items]
Long-term Debt, gross	$ 0.2	0.5
Interest rate, stated percentage	5.00%
Capital Lease Obligations | Foreign 10.7% due 2018 to 2036
Debt Instrument [Line Items]
Long-term Debt, gross	$ 10.6	$ 9.7
Interest rate, stated percentage	10.70%