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Derivatives (Realized and Unrealized Gains (Losses) with Respect to Cash Flow Hedges) (Details) CAD in Millions, $ in Millions | 12 Months Ended
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Dec. 31, 2016 CAD | Dec. 31, 2016 USD ($) | Dec. 31, 2015 CAD | Dec. 31, 2015 USD ($)
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Unrealized Gain (Loss) on Derivatives | CAD | CAD (258) |  | CAD (96) |
Other Derivatives Hedge [Member] | Interest Rate Swap [Member] | Line of Credit [Member] | Brunswick Pipeline [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Convertible Subordinated Debt | CAD | CAD 250 |  |  |
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative, Gain (Loss) on Derivative, Net |  | $ 2 |  | $ (3)
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Other Operating Income (Expense) [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Unrealized Gain (Loss) on Derivatives |  | 0 |  | 0
Derivative, Gain (Loss) on Derivative, Net |  | 0 |  | 0
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member] | Interest Expense [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Unrealized Gain (Loss) on Derivatives |  | 2 |  | (3)
Designated as Hedging Instrument [Member] | Foreign Exchange Option [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Derivative, Gain (Loss) on Derivative, Net |  | $ (87) |  | 92
Designated as Hedging Instrument [Member] | Foreign Exchange Option [Member] | TECO Energy Inc [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Line of Credit Facility, Expiration Date | Dec. 31, 2019 | Dec. 31, 2019 |  |
Derivative, Notional Amount | CAD | CAD 1,519 |  |  |
Designated as Hedging Instrument [Member] | Foreign Exchange Option [Member] | Other Operating Income (Expense) [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Unrealized Gain (Loss) on Derivatives |  | $ (87) |  | 0
Derivative, Gain (Loss) on Derivative, Net |  | 0 |  | 92
Designated as Hedging Instrument [Member] | Foreign Exchange Option [Member] | Interest Expense [Member] |  |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |  |
Unrealized Gain (Loss) on Derivatives |  | $ 0 |  | $ 0

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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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- Definition Including the current and noncurrent portions, the carrying value of convertible subordinated debt, as of the balance sheet date, initially scheduled to be repaid after one year or beyond the normal operating cycle if longer. This form of debt can be exchanged for a specified amount of another security, typically the entity's common stock, at the option of the issuer or the holder, and places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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- Definition Amount of increase (decrease) in the fair value of derivatives recognized in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5618551-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (a),(c),(d),(e) -URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5624171-113959 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Date the credit facility terminates, in CCYY-MM-DD format. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585 + Details
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