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Acquision (Related Expenses and Pro Forma Data) (Details) - TECO Energy Inc [Member] - CAD CAD in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2016 | Dec. 31, 2015
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |
Business Combination, Acquisition Related Costs |  |  | CAD 166 | CAD 53
Business Acquisition, Pro Forma Information [Abstract] |  |  |  |
Pro forma operating revenues |  |  | 6,034 | 6,297
Prop forma net income attributable to common shareholders |  |  | 386 | 584
Adjusted pro forma operating revenues increased | CAD 10 | CAD 10 | 10 | 10
Business Acquisitions Pro Forma Increase To Net Income Loss |  |  | 53 | (35)
New Mexico |  |  |  |
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |
Business Combination, Acquisition Related Costs |  |  | 23 |
Sales [Member] |  |  |  |
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |
Business Combination, Acquisition Related Costs |  |  | (10) | 0
Sales [Member] | New Mexico |  |  |  |
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |
Business Combination, Acquisition Related Costs |  |  | (10) |
Operating Expense [Member] |  |  |  |
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |
Business Combination, Acquisition Related Costs |  |  | 89 | 52
Operating Expense [Member] | New Mexico |  |  |  |
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |
Business Combination, Acquisition Related Costs |  |  | 30 |
Interest Expense [Member] |  |  |  |
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |
Business Combination, Acquisition Related Costs |  |  | 148 | 24
Other Operating Income (Expense) [Member] |  |  |  |
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |
Business Combination, Acquisition Related Costs |  |  | (3) | 0
Before Tax [Member] |  |  |  |
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |
Business Combination, Acquisition Related Costs |  |  | 250 | 76
Before Tax [Member] | New Mexico |  |  |  |
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |
Business Combination, Acquisition Related Costs |  |  | 40 |
Income Tax Expense [Member] |  |  |  |
Business Combination, Separately Recognized Transactions [Line Items] |  |  |  |
Business Combination, Acquisition Related Costs |  |  | CAD (84) | CAD (23)

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