Retirement Benefits - Estimated OPEB Future Ben Pmts (Details) $ in Millions	Dec. 31, 2019 USD ($)
Retirement benefits other than pension
Estimated Future Benefits Payments [Line Items]
2020	$ 41.2
2021	40.5
2022	39.3
2023	38.3
2024	37.0
2025 through 2029	165.6
UMWA Plans
Estimated Future Benefits Payments [Line Items]
2020	30.2
2021	30.2
2022	29.7
2023	29.3
2024	28.7
2025 through 2029	132.2
Black Lung and Other Plans
Estimated Future Benefits Payments [Line Items]
2020	11.0
2021	10.3
2022	9.6
2023	9.0
2024	8.3
2025 through 2029	$ 33.4

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- Definition

Amount of benefits for defined benefit plan expected to be paid in five fiscal years after fifth fiscal year following latest fiscal year.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

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Amount of benefits for defined benefit plan expected to be paid in next fiscal year following latest fiscal year.

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Amount of benefits for defined benefit plan expected to be paid in fifth fiscal year following latest fiscal year.

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Amount of benefits for defined benefit plan expected to be paid in fourth fiscal year following latest fiscal year.

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Amount of benefits for defined benefit plan expected to be paid in third fiscal year following latest fiscal year.

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Amount of benefits for defined benefit plan expected to be paid in second fiscal year following latest fiscal year.

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