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Derivatives and Risk Management Activities - Currency Exchange Rate Risk Hedging (Details) $ in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) $ / $	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) $ / $	Sep. 30, 2019 USD ($)	Sep. 30, 2020 CAD ($) $ / $	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 \| $	$ 2	$ (1)	$ (2)	$ 6
Forward exchange contracts that exchange CAD For USD maturing in 2020
Currency Exchange Rate Risk Hedging:
Notional amount of derivatives	$ 153		$ 153		$ 205
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		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)	1.34		1.34		1.34
Forward exchange contracts that exchange USD for CAD maturing in 2020
Currency Exchange Rate Risk Hedging:
Notional amount of derivatives	$ 88		$ 88		$ 118
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		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)	1.34		1.34		1.34
Forward exchange contracts that exchange USD for CAD maturing in 2021
Currency Exchange Rate Risk Hedging:
Notional amount of derivatives	$ 21		$ 21		$ 28
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		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)	1.32		1.32		1.32
Interest Rate Derivatives \| Derivatives in Hedging Relationships \| Other current liabilities
Currency Exchange Rate Risk Hedging:
Derivative liability \| $						$ 1
Interest Rate Derivatives \| Derivatives in Hedging Relationships \| Other current liabilities \| Maximum
Currency Exchange Rate Risk Hedging:
Derivative liability \| $	$ 1		$ 1
Interest Rate Derivatives \| Derivatives in Hedging Relationships \| Other current assets
Currency Exchange Rate Risk Hedging:
Derivative asset \| $						$ 2
Interest Rate Derivatives \| Derivatives in Hedging Relationships \| Other current assets \| Maximum
Currency Exchange Rate Risk Hedging:
Derivative asset \| $	$ 1		$ 1