Retirement Benefits (Pension Plan Assets at Fair Value by Asset Class) (Details) - Defined Benefit Pension Plan - USD ($) $ in Millions	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 246.6	$ 256.5	$ 254.1
U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,343.7	3,048.3	2,832.4
U.S. | Total U.S. Qualified Pension Plans at Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,157.8	2,878.6
U.S. | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14.8	16.9
U.S. | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	325.3	573.9
U.S. | Equity mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	243.4	213.1
U.S. | Equity pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	448.7	762.0
U.S. | Bonds (government and corporate)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,125.6	1,312.7
U.S. | Real estate pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	185.9	169.7
U.S. | Level 1 | Total U.S. Qualified Pension Plans at Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	583.5	803.9
U.S. | Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14.8	16.9
U.S. | Level 1 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	325.3	573.9
U.S. | Level 1 | Equity mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	243.4	213.1
U.S. | Level 1 | Equity pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
U.S. | Level 1 | Bonds (government and corporate)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
U.S. | Level 2 | Total U.S. Qualified Pension Plans at Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,574.3	2,074.7
U.S. | Level 2 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
U.S. | Level 2 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
U.S. | Level 2 | Equity mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
U.S. | Level 2 | Equity pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	448.7	762.0
U.S. | Level 2 | Bonds (government and corporate)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,125.6	1,312.7
U.S. | Level 3 | Total U.S. Qualified Pension Plans at Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
U.S. | Level 3 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
U.S. | Level 3 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
U.S. | Level 3 | Equity mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
U.S. | Level 3 | Equity pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
U.S. | Level 3 | Bonds (government and corporate)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
International
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,905.0	1,726.8	$ 1,672.4
International | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16.8	13.9
International | Equity pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	676.4	746.8
International | Fixed income pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	948.5	694.1
International | Other pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16.7	15.5
International | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	246.6	256.5
International | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16.8	13.9
International | Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16.8	13.9
International | Level 1 | Equity pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
International | Level 1 | Fixed income pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
International | Level 1 | Other pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
International | Level 1 | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
International | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,641.6	1,456.4
International | Level 2 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
International | Level 2 | Equity pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	676.4	746.8
International | Level 2 | Fixed income pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	948.5	694.1
International | Level 2 | Other pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16.7	15.5
International | Level 2 | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
International | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	246.6	256.5
International | Level 3 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
International | Level 3 | Equity pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
International | Level 3 | Fixed income pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
International | Level 3 | Other pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
International | Level 3 | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 246.6	$ 256.5