Retirement Benefits (Pension Plan Assets at Fair Value by Asset Class) (Details) - Defined Benefit Pension Plan - USD ($) $ in Millions	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 303.7	$ 301.4	$ 260.0
Level 3 | Alternative credit pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	115.4	113.6	94.2
Level 3 | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	188.3	187.8	165.8
U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,409.0	2,533.0	2,299.0
U.S. | Total U.S. Qualified Pension Plans at Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,143.9	2,384.1
U.S. | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	15.4	14.7
U.S. | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	271.5	320.0
U.S. | Equity pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	109.3	204.7
U.S. | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,747.7	1,844.7
U.S. | Real estate pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	129.5	148.9
U.S. | Alternative credit pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	135.6	0.0
U.S. | Level 1 | Total U.S. Qualified Pension Plans at Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	286.9	334.7
U.S. | Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	15.4	14.7
U.S. | Level 1 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	271.5	320.0
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	1,857.0	2,049.4
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 pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	109.3	204.7
U.S. | Level 2 | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,747.7	1,844.7
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 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	1,318.6	1,374.5	$ 1,134.0
International | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5.4	3.6
International | Equity pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	180.4	192.1
International | Fixed income pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	810.2	858.0
International | Alternative credit pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	115.4	113.6
International | Other pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	18.9	19.4
International | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	188.3	187.8
International | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5.4	3.6
International | Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5.4	3.6
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 | Alternative credit 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	1,009.5	1,069.5
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	180.4	192.1
International | Level 2 | Fixed income pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	810.2	858.0
International | Level 2 | Alternative credit pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
International | Level 2 | Other pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	18.9	19.4
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	303.7	301.4
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 | Alternative credit pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	115.4	113.6
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	$ 188.3	$ 187.8