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Derivatives and Risk Management Activities - Currency Exchange Rate Risk Hedging (Details) $ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) $ / $	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2020 CAD ($) $ / $
Foreign Currency Derivatives \| Supply and Logistics segment revenues \| Derivatives Not Designated as a Hedge
Currency Exchange Rate Risk Hedging:
Gain/(loss) recognized in earnings \| $	$ 1	$ 8	$ (23)
Forward exchange contracts that exchange CAD for USD maturing in 2021
Currency Exchange Rate Risk Hedging:
Notional amount of derivatives	$ 46			$ 59
Forward exchange contracts that exchange CAD for USD maturing in 2021 \| 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 2021 \| Maximum
Currency Exchange Rate Risk Hedging:
Average exchange rate (cad per usd) \| $ / $	1.28			1.28
Forward exchange contracts that exchange USD for CAD maturing in 2021
Currency Exchange Rate Risk Hedging:
Notional amount of derivatives	$ 80			$ 104
Forward exchange contracts that exchange USD for CAD maturing in 2021 \| 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 2021 \| Maximum
Currency Exchange Rate Risk Hedging:
Average exchange rate (cad per usd) \| $ / $	1.30			1.30
Interest Rate Derivatives \| Other current assets \| Derivatives in Hedging Relationships
Currency Exchange Rate Risk Hedging:
Derivative asset \| $		2
Interest Rate Derivatives \| Other current assets \| Maximum \| Derivatives in Hedging Relationships
Currency Exchange Rate Risk Hedging:
Derivative asset \| $	$ 2
Interest Rate Derivatives \| Other current liabilities \| Derivatives in Hedging Relationships
Currency Exchange Rate Risk Hedging:
Derivative liability \| $		$ 1