Risk Management - Net Investment Hedging Effect on the Income Statements (Details) - Net Investment Hedging - Designated as Hedging Instrument - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Gain/(loss) recognized in OCI on derivative	$ 0	$ (8)	$ 91
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0	83	26
Foreign Exchange Contract [Member]
Derivative [Line Items]
Gain/(loss) recognized in OCI on derivative	0	(8)	91
Loss (gain) on impairments and divestitures, net \| Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ 0	83	26
KML and U.S. Portion of Cochin Pipeline System \| Foreign Exchange Contract [Member]
Derivative [Line Items]
Gain/(loss) reclassified from Accumulated OCI into income		$ 83
Trans Mountain and Trans Mountain Expansion Project \| Foreign Exchange Contract [Member]
Derivative [Line Items]
Gain/(loss) reclassified from Accumulated OCI into income			$ 26

The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

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