Debt (Long-term Debt) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Debt Instrument [Line Items]
Long-term Debt, gross	$ 7,950.2	$ 3,274.8
Less: Unamortized discount and debt issuance costs	(55.8)	(12.2)
Less: Fair value hedge accounting adjustments	5.7	5.2
Total Long-term Debt	7,900.1	3,267.8
Less: Current portion of long-term debt	(470.0)	(40.4)
Less: Long-term debt – related party	(297.2)	(320.1)
Long-term Debt	7,132.9	2,907.3
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
Debt Instrument [Line Items]
Less: Unamortized discount and debt issuance costs	$ (45.0)
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%
Senior Notes \| Note 1.50% due 2026
Debt Instrument [Line Items]
Long-term Debt, gross	$ 550.0	0.0
Interest rate, stated percentage	1.50%
Senior Notes \| Note 1.85% due 2027
Debt Instrument [Line Items]
Long-term Debt, gross	$ 650.0	0.0
Interest rate, stated percentage	1.85%
Senior Notes \| Note 2.05% due 2030
Debt Instrument [Line Items]
Long-term Debt, gross	$ 900.0	0.0
Interest rate, stated percentage	2.05%
Senior Notes \| Note 2.70% due 2040
Debt Instrument [Line Items]
Long-term Debt, gross	$ 750.0	0.0
Interest rate, stated percentage	2.70%
Senior Notes \| Note 2.80% due 2050
Debt Instrument [Line Items]
Long-term Debt, gross	$ 950.0	0.0
Interest rate, stated percentage	2.80%
Bonds \| Variable-rate industrial revenue bonds 0.1% due 2035 to 2050
Debt Instrument [Line Items]
Long-term Debt, gross	$ 631.9	631.9
Interest rate, weighted average	0.10%
Bonds \| Eurobonds 2.0% due 2020
Debt Instrument [Line Items]
Long-term Debt, gross	$ 0.0	327.0
Interest rate, stated percentage	2.00%
Bonds \| Eurobonds 0.375% due 2021
Debt Instrument [Line Items]
Long-term Debt, gross	$ 410.3	381.5
Interest rate, stated percentage	0.375%
Bonds \| Eurobonds 1.0% due 2025
Debt Instrument [Line Items]
Long-term Debt, gross	$ 351.7	327.0
Interest rate, stated percentage	1.00%
Bonds \| Eurobonds 0.50% due 2028
Debt Instrument [Line Items]
Long-term Debt, gross	$ 586.2	0.0
Interest rate, stated percentage	0.50%
Bonds \| Eurobonds 0.80% due 2032
Debt Instrument [Line Items]
Long-term Debt, gross	$ 586.2	0.0
Interest rate, stated percentage	0.80%
Bonds \| Other Foreign 0% due 2023
Debt Instrument [Line Items]
Long-term Debt, gross	$ 0.6	3.8
Related Party \| Chinese Renminbi 5.5% due 2021 to 2027
Debt Instrument [Line Items]
Long-term Debt, gross	$ 338.5	357.9
Interest rate, stated percentage	5.50%
Capital Lease Obligations \| Foreign 10.9% due 2021 to 2036
Debt Instrument [Line Items]
Long-term Debt, gross	$ 9.2	$ 10.1
Interest rate, weighted average	10.90%

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount of cumulative increase (decrease) in fair value of hedged liability in fair value hedge, attributable to hedged risk.

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Amount of long-term debt and lease obligation, classified as noncurrent.

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The amount for notes payable (written promise to pay), payable to related parties, which are due after one year (or one business cycle).

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