Acquisition (Purchase Consideration) (Details) - TECO Energy Inc [Member] $ / shares in Units, CAD in Millions, $ in Millions	Jul. 01, 2016 CAD	Jul. 01, 2016 USD ($)	Aug. 02, 2016 CAD	Jul. 01, 2016 USD ($) $ / shares
Business Combination, Consideration Transferred [Abstract]
Business Acquisition, Share Price				$ 27.55
Payments to Acquire Businesses, Gross	CAD 8,400	$ 6,500
Business Combination, Consideration Transferred, Liabilities Incurred	5,500	4,200
Business Combination, Consideration Transferred	13,900	$ 10,700
Short-Term Debt/Long-Term Debt [Abstract]
Convertible Debt	728		CAD 1,400	$ 560
Junior Subordinated Notes, Noncurrent	1,560			1,200
Other Long-term Debt, Noncurrent	500			384
Senior Notes, Noncurrent	4,200			3,250
Line of Credit Facility, Fair Value of Amount Outstanding	CAD 1,400			$ 1,100

Price of a single share of a number of saleable stocks paid or offered to be paid in a business combination.

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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Amount of liabilities incurred by the acquirer as part of consideration transferred in a business combination.

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Including the current and noncurrent portions, carrying amount of debt identified as being convertible into another form of financial instrument (typically the entity's common stock) as of the balance sheet date, which originally required full repayment more than twelve months after issuance or greater than the normal operating cycle of the company.

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Carrying value as of the balance sheet date of long-term debt (with maturities initially due after one year or beyond the operating cycle if longer) identified as Junior Subordinated Notes, which have a lower priority than senior instruments, excluding current portion.

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Fair value of the amount outstanding under the credit facility.

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Amount of long-term debt classified as other, payable after one year or the operating cycle, if longer.

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The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

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Carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion. Senior note holders are paid off in full before any payments are made to junior note holders.

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