Employee Benefit Plans - Schedule of Amounts Recognized in Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Pension Benefits
Recognized in accumulated other comprehensive income (loss) as of September 30 (net of taxes)
Net actuarial (loss) gain	$ (89.0)	$ (68.9)
Prior service (cost) benefit	(13.4)	(7.0)
Total	(102.4)	(75.9)
Postretirement Health and Other
Recognized in accumulated other comprehensive income (loss) as of September 30 (net of taxes)
Net actuarial (loss) gain	(6.1)	(1.9)
Prior service (cost) benefit	12.6	8.4
Total	$ 6.5	$ 6.5

Amount, after tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Amount, after tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

Amount, after tax, of accumulated other comprehensive (income) loss for cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
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-Paragraph 1
-Subparagraph (j)
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