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Derivatives and Risk Management Activities - Currency Exchange Rate Risk Hedging (Details) $ in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($) $ / $	Mar. 31, 2019 USD ($)	Mar. 31, 2020 CAD ($) $ / $	Dec. 31, 2019 USD ($)
Foreign Currency Derivatives \| Derivatives Not Designated as a Hedge \| Supply and Logistics segment revenues
Currency Exchange Rate Risk Hedging:
Gain/(loss) recognized in earnings \| $	$ (6)	$ 5
Forward exchange contracts that exchange CAD For USD maturing in 2020
Currency Exchange Rate Risk Hedging:
Notional amount of derivatives	$ 132		$ 175
Forward exchange contracts that exchange CAD For USD maturing in 2020 \| Minimum
Currency Exchange Rate Risk Hedging:
Average exchange rate (cad per usd)	1.00		1.00
Forward exchange contracts that exchange CAD For USD maturing in 2020 \| Maximum
Currency Exchange Rate Risk Hedging:
Average exchange rate (cad per usd)	1.32		1.32
Forward exchange contracts that exchange USD for CAD maturing in 2020
Currency Exchange Rate Risk Hedging:
Notional amount of derivatives	$ 300		$ 404
Forward exchange contracts that exchange USD for CAD maturing in 2020 \| Minimum
Currency Exchange Rate Risk Hedging:
Average exchange rate (cad per usd)	1.00		1.00
Forward exchange contracts that exchange USD for CAD maturing in 2020 \| Maximum
Currency Exchange Rate Risk Hedging:
Average exchange rate (cad per usd)	1.35		1.35
Interest Rate Derivatives \| Derivatives in Hedging Relationships \| Other current assets
Currency Exchange Rate Risk Hedging:
Derivative asset \| $	$ 1			$ 2
Interest Rate Derivatives \| Derivatives in Hedging Relationships \| Other current liabilities
Currency Exchange Rate Risk Hedging:
Derivative liability \| $	$ 6			$ 1