Retirement Benefits (Pension Plan Assets at Fair Value by Asset Class) (Details) - Defined Benefit Pension Plan - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 260.0	$ 209.0	$ 246.6
Level 3 | Fixed income pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	94.2	53.5	0.0
Level 3 | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	165.8	155.5	246.6
U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,299.0	2,404.0	3,343.7
U.S. | Total U.S. Qualified Pension Plans at Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,112.4	2,173.4
U.S. | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14.6	14.0
U.S. | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	143.0	127.4
U.S. | Equity mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	105.2	84.5
U.S. | Equity pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	187.8	188.4
U.S. | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,661.8	1,759.1
U.S. | Real estate pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	186.6	230.6
U.S. | Level 1 | Total U.S. Qualified Pension Plans at Fair Value
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	262.8	225.9
U.S. | Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14.6	14.0
U.S. | Level 1 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	143.0	127.4
U.S. | Level 1 | Equity mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	105.2	84.5
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	1,849.6	1,947.5
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	187.8	188.4
U.S. | Level 2 | Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,661.8	1,759.1
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	1,134.0	1,122.0	$ 1,905.0
International | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8.0	12.1
International | Equity pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	218.5	348.1
International | Fixed income pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	724.6	589.9
International | Other pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17.1	16.4
International | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	165.8	155.5
International | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8.0	12.1
International | Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8.0	12.1
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	866.0	900.9
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	218.5	348.1
International | Level 2 | Fixed income pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	630.4	536.4
International | Level 2 | Other pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17.1	16.4
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	260.0	209.0
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	94.2	53.5
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	$ 165.8	$ 155.5