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Lease Commitments - Narrative (Details) $ in Millions | 12 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Dec. 31, 2019 USD ($) MW | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | May 16, 2019 MW | Dec. 31, 2016 MW | Aug. 31, 2016 MW | Jan. 15, 2016 lease | Jan. 15, 2015 lease
Lessee, Lease, Description [Line Items] |  |  |  |  |  |  |  |
Unamortized cost of prepaid right-of-way agreements | $ 60.2 | $ 63.0 |  |  |  |  |  |
Amortization of prepaid right-of-way agreements | 3.7 | $ 3.8 | $ 3.5 |  |  |  |  |
Operating leases, capitalized financing costs, investing activities | 3.9 |  |  |  |  |  |  |
Finance leases, capitalized financing costs, investing activities | 0.7 |  |  |  |  |  |  |
Lessee, operating lease, unguaranteed residual value | 21.8 |  |  |  |  |  |  |
Public Service Company of New Mexico |  |  |  |  |  |  |  |
Lessee, Lease, Description [Line Items] |  |  |  |  |  |  |  |
Operating leases, capitalized financing costs, investing activities | 1.3 |  |  |  |  |  |  |
Finance leases, capitalized financing costs, investing activities | 0.3 |  |  |  |  |  |  |
Lessee, operating lease, unguaranteed residual value | 8.7 |  |  |  |  |  |  |
Texas-New Mexico Power Company |  |  |  |  |  |  |  |
Lessee, Lease, Description [Line Items] |  |  |  |  |  |  |  |
Operating leases, capitalized financing costs, investing activities | 2.6 |  |  |  |  |  |  |
Finance leases, capitalized financing costs, investing activities | 0.4 |  |  |  |  |  |  |
Lessee, operating lease, unguaranteed residual value | 13.1 |  |  |  |  |  |  |
Palo Verde Nuclear Generating Station, Units 1 And 4 | Public Service Company of New Mexico |  |  |  |  |  |  |  |
Lessee, Lease, Description [Line Items] |  |  |  |  |  |  |  |
Number of leases expiring | lease |  |  |  |  |  |  |  | 4
Number of leases under which lease term was extended | lease |  |  |  |  |  |  |  | 4
Annual lease payments during renewal period | 16.5 |  |  |  |  |  |  |
Palo Verde Nuclear Generating Station, Unit 2 | Public Service Company of New Mexico |  |  |  |  |  |  |  |
Lessee, Lease, Description [Line Items] |  |  |  |  |  |  |  |
Number of leases expiring | lease |  |  |  |  |  |  | 4 |
Number of leases under which lease term was extended | lease |  |  |  |  |  |  | 1 |
Annual lease payments during renewal period | $ 1.6 |  |  |  |  |  |  |
Number of megawatts purchased (in megawatts) | MW |  |  |  |  |  | 64.1 |  |
Number of megawatts (in megawatts) | MW |  |  |  | 114.6 | 114.6 | 114.6 |  |
Palo Verde Nuclear Generating Station | Public Service Company of New Mexico |  |  |  |  |  |  |  |
Lessee, Lease, Description [Line Items] |  |  |  |  |  |  |  |
Lease covenant, restriction on conveying, transferring, leasing and dividends | 5.00% |  |  |  |  |  |  |
Loss contingency, range of possible loss, portion not accrued | $ 157.6 |  |  |  |  |  |  |
Navajo Nation | Public Service Company of New Mexico |  |  |  |  |  |  |  |
Lessee, Lease, Description [Line Items] |  |  |  |  |  |  |  |
Right-of-way lease, annual payments | 6.0 |  |  |  |  |  |  |
Right-of-way lease, payments | $ 6.9 |  |  |  |  |  |  |
New Mexico 2015 Rate Case | Palo Verde Nuclear Generating Station, Unit 2 | Public Service Company of New Mexico |  |  |  |  |  |  |  |
Lessee, Lease, Description [Line Items] |  |  |  |  |  |  |  |
Number of megawatts purchased (in megawatts) | MW | 64.1 |  |  | 64.1 |  |  |  |
Equipment |  |  |  |  |  |  |  |
Lessee, Lease, Description [Line Items] |  |  |  |  |  |  |  |
Operating lease, residual value of leased asset | $ 1.9 |  |  |  |  |  |  |
Equipment | Public Service Company of New Mexico |  |  |  |  |  |  |  |
Lessee, Lease, Description [Line Items] |  |  |  |  |  |  |  |
Operating lease, residual value of leased asset | 0.7 |  |  |  |  |  |  |
Equipment | Texas-New Mexico Power Company |  |  |  |  |  |  |  |
Lessee, Lease, Description [Line Items] |  |  |  |  |  |  |  |
Operating lease, residual value of leased asset | $ 1.2 |  |  |  |  |  |  |

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