Retirement Benefits (Pension Plan Assets at Fair Value by Asset Class) (Details) - Defined Benefit Pension Plan - USD ($) $ in Millions	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 301.4	$ 260.0	$ 209.0
Level 3 | Fixed income pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	113.6	94.2	53.5
Level 3 | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	187.8	165.8	155.5
U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,533.0	2,299.0	2,404.0
U.S. | Total U.S. Qualified Pension Plans at Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,384.1	2,112.4
U.S. | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14.7	14.6
U.S. | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	320.0	143.0
U.S. | Equity mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	105.2
U.S. | Equity pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	204.7	187.8
U.S. | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,844.7	1,661.8
U.S. | Real estate pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	148.9	186.6
U.S. | Level 1 | Total U.S. Qualified Pension Plans at Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	334.7	262.8
U.S. | Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14.7	14.6
U.S. | Level 1 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	320.0	143.0
U.S. | Level 1 | Equity mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	105.2
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 | Fixed income securities
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	2,049.4	1,849.6
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	204.7	187.8
U.S. | Level 2 | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,844.7	1,661.8
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 | Fixed income securities
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	1,374.5	1,134.0	$ 1,122.0
International | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3.6	8.0
International | Equity pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	192.1	218.5
International | Fixed income pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	971.6	724.6
International | Other pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	19.4	17.1
International | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	187.8	165.8
International | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3.6	8.0
International | Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3.6	8.0
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	1,069.5	866.0
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	192.1	218.5
International | Level 2 | Fixed income pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	858.0	630.4
International | Level 2 | Other pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	19.4	17.1
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	301.4	260.0
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	113.6	94.2
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	$ 187.8	$ 165.8