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Commitments, Guarantees and Contingencies Minimum Payments for Certain Long-Term Commitments (Details) $ in Millions | Dec. 31, 2018 USD ($)
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Coal, Rail and Shipping Contracts [Member] |  |
Minimum Annual Payments for Certain Long-Term Commitments [Line Items] |  |
Minimum Payments in 2019 | $ 20.8 |
Minimum Payments in 2020 | 9.0 |
Minimum Payments in 2021 | 7.5 |
Minimum Payments in 2022 | 0.0 |
Minimum Payments in 2023 | 0.0 |
Minimum Payments Thereafter | 0.0 |
Leasing Agreements [Member] |  |
Minimum Annual Payments for Certain Long-Term Commitments [Line Items] |  |
Minimum Payments in 2019 | 9.9 |
Minimum Payments in 2020 | 7.9 |
Minimum Payments in 2021 | 6.1 |
Minimum Payments in 2022 | 4.9 |
Minimum Payments in 2023 | 3.1 |
Minimum Payments Thereafter | 9.4 |
Easements [Member] |  |
Minimum Annual Payments for Certain Long-Term Commitments [Line Items] |  |
Minimum Payments in 2019 | 4.8 |
Minimum Payments in 2020 | 4.9 |
Minimum Payments in 2021 | 4.9 |
Minimum Payments in 2022 | 5.0 |
Minimum Payments in 2023 | 5.1 |
Minimum Payments Thereafter | 136.3 |
Long-Term Service Agreements [Member] |  |
Minimum Annual Payments for Certain Long-Term Commitments [Line Items] |  |
Minimum Payments in 2019 | 31.6 | [1]
Minimum Payments in 2020 | 0.3 | [1]
Minimum Payments in 2021 | 0.3 | [1]
Minimum Payments in 2022 | 0.0 | [1]
Minimum Payments in 2023 | 0.0 | [1]
Minimum Payments Thereafter | 0.1 | [1]
PPAs [Member] |  |
Minimum Annual Payments for Certain Long-Term Commitments [Line Items] |  |
Minimum Payments in 2019 | 107.3 | [2]
Minimum Payments in 2020 | 115.3 | [2]
Minimum Payments in 2021 | 145.4 | [2]
Minimum Payments in 2022 | 145.7 | [2]
Minimum Payments in 2023 | 145.8 | [2]
Minimum Payments Thereafter | $ 1,550.7 | [2]
[1] | Consists of long-term service agreements for wind energy facilities.
[2] | Does not include the agreement with Manitoba Hydro expiring in 2022, as this contract is for surplus energy only; Oliver Wind I and Oliver Wind II, as Minnesota Power only pays for energy as it is delivered; and the agreement with Nobles 2 commencing in 2020 as it is subject to construction of a wind energy facility. (See Power Purchase Agreements.)

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- Definition Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=77902758&loc=d3e41502-112717 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 10 -Section 55 -Paragraph 40 -Subparagraph (Note 3) -URI http://asc.fasb.org/extlink&oid=82846649&loc=d3e38371-112697 + Details
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- Definition Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 10 -Section 55 -Paragraph 40 -Subparagraph (Note 3) -URI http://asc.fasb.org/extlink&oid=82846649&loc=d3e38371-112697 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=77902758&loc=d3e41502-112717 + Details
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- Definition Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 10 -Section 55 -Paragraph 40 -Subparagraph (Note 3) -URI http://asc.fasb.org/extlink&oid=82846649&loc=d3e38371-112697 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=77902758&loc=d3e41502-112717 + Details
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