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Pension and Savings Plans - Textual (Details) | 3 Months Ended | 12 Months Ended
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Apr. 01, 2017 numberOfPlan | Dec. 31, 2021 | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Number of 401(k) plans | numberOfPlan | 3 |  |  |  |
Paid discretionary contributions to defined contribution pension plans, company match |  |  | $ 9,600,000 | $ 27,800,000 | $ 30,300,000
Discretionary contributions to defined contribution pension plans, granted |  |  | 0 | 0 |
Payment of prior performance contributions |  |  | 0 | 8,900,000 | 8,500,000
Australia |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Paid discretionary contributions to defined contribution pension plans, company match |  |  | 20,500,000 | 26,500,000 | 31,600,000
Discretionary contributions to defined contribution pension plans, granted |  |  | 0 | 0 |
Payment of prior performance contributions |  |  | 0 | 3,000,000 | 3,000,000
Pension Plan |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Payment for settlement |  |  | 51,600,000 | 0 |
Settlement gain |  |  | $ 2,700,000 | $ 0 | $ 0
Expected long-term return on plan assets |  |  | 3.60% | 4.20% | 5.65%
Accumulated benefit obligation |  |  | $ 816,400,000 | $ 853,800,000 |
Defined benefit plan, assets |  |  | $ 847,500,000 | 855,200,000 | $ 764,800,000
Percentage of company's qualified pension plans on a GAAP accounting basis |  |  | 80.00% |  |
Peabody Plan |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined benefit plan, assets |  |  | $ 672,500,000 | 689,400,000 |
Plan with accumulated benefit obligation in excess of plan assets, accumulated benefit obligation |  |  | 632,900,000 | 675,900,000 |
Western Plan |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined benefit plan, assets |  |  | 175,000,000.0 | 165,800,000 |
Plan with accumulated benefit obligation in excess of plan assets, accumulated benefit obligation |  |  | $ 183,500,000 | $ 177,900,000 |
Fixed Income Investments |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Plan assets, target allocation, percentage |  |  | 100.00% |  |
Real Estate |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Plan assets, target allocation, percentage |  |  | 1.00% | 1.00% |
Scenario, Forecast | Pension Plan |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Expected long-term return on plan assets |  | 2.80% |  |  |

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- Definition Paid discretionary contributions to defined contribution pension plans, company match. + References No definition available. + Details
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- Definition Percentage of company's qualified pension plans on a GAAP accounting basis. + References No definition available. + Details
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- Definition Amount of payment, which decreases benefit obligation of defined benefit plan, for irrevocable action relieving primary responsibility for benefit obligation and eliminating risk for obligation and assets used to effect settlement. Transaction constituting settlement includes, but is not limited to, making lump-sum cash payment to participant in exchange for their rights to receive specified benefits and purchasing nonparticipating annuity contract. Excludes decreases to benefit obligation for remeasurement due to settlement. + 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 (a)(10) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 30 -Section 15 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=7577095&loc=d3e8001-114927 + Details
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