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Commitments - Fiscal Year Maturity (Footnotes) (Details) CAD in Millions, $ in Millions | 1 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Apr. 30, 2015 MW | Dec. 31, 2016 USD ($) GWh lease contract agreement_renewal MW | Dec. 31, 2016 CAD
Long-term Purchase Commitment [Line Items] |  |  |
Agreement Renewal, Number | agreement_renewal |  | 10,000,000 |
Agreement Renewal, Term |  | 50 years |
UNS Energy Corporation | Springerville Common Facilities |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Capital leases, undivided leased interest, percentage |  | 32.20% |
Fixed purchase price | $ |  | $ 68 |
Leases, Number | lease |  | 2 |
Power |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Purchase obligation |  |  | CAD 2,295
Power | FortisOntario |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Purchase obligation |  |  | 743
Power | FortisOntario | Maximum |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Amount of volume required (in mw) | MW |  | 145,000,000 |
Power | FortisOntario | Minimum |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Volume of energy required to be purchased (in GWh) | GWh |  | 537 |
Power | FortisBC Energy |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Purchase obligation |  |  | 486
Power | FortisBC Electric |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Purchase obligation |  |  | 288
Long-term renewable PPA, term |  | 20 years |
Amount of volume required (in mw) | MW | 234 |  |
Power | FortisBC Electric | Maximum |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Amount of volume required (in mw) | MW |  | 200 |
Volume of energy required to be purchased (in GWh) | GWh |  | 1,752 |
Power | Maritime Electric |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Number of long-term take-or-pay contracts | contract |  | 2 |
Power | Maritime Electric | Nuclear Generating Station |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Share of plant output, percentage |  | 4.55% |
Power | Payment guarantee | Maritime Electric |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Purchase obligation |  |  | 480
WECA | FortisBC Electric |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Long-term renewable PPA, term | 40 years |  |
Renewable Power |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Purchase obligation |  |  | 1,625
Renewable Power | TEP and UNS Electric, Inc |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Purchase obligation | $ |  | $ 1,210 |
Purchase commitment, percentage |  | 100.00% |
Take-or-pay contract | FortisOntario |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Amount of volume required (in mw) | MW |  | 145,000,000 |
Coal | UNS Energy Corporation |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Purchase obligation | $ |  | $ 496 |
Gas Transportation Services | UNS Energy Corporation |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Purchase obligation | $ |  | 244 |
Transmission Services | UNS Energy Corporation |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Purchase obligation | $ |  | 113 |
Renewable Energy Credit |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Purchase obligation |  |  | CAD 154
Renewable Energy Credit | UNS Energy Corporation |  |  |
Long-term Purchase Commitment [Line Items] |  |  |
Purchase obligation | $ |  | $ 107 |

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