Retirement Benefits - Estimated OPEB Future Ben Pmts (Details) $ in Millions	Dec. 31, 2018 USD ($)
Retirement benefits other than pension
Estimated Future Benefits Payments [Line Items]
2019	$ 41.3
2020	40.9
2021	40.4
2022	40.6
2023	39.9
2024 through 2028	186.2
UMWA Plans
Estimated Future Benefits Payments [Line Items]
2019	33.5
2020	33.6
2021	33.6
2022	34.2
2023	34.0
2024 through 2028	161.8
Black Lung and Other Plans
Estimated Future Benefits Payments [Line Items]
2019	7.8
2020	7.3
2021	6.8
2022	6.4
2023	5.9
2024 through 2028	$ 24.4

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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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