Risk Management - Derivatives in Net Investment Hedging Relationships (Details) - Derivatives in net investment hedging relationships - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Gain/(loss) recognized in OCI on derivative	$ 0	$ (14)	$ (8)	$ (14)
Gain/(loss) reclassified from Accumulated OCI into income	0	26	0	26
Foreign currency contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain/(loss) recognized in OCI on derivative	0	(14)	(8)	(14)
Foreign currency contracts | (Gain) loss on divestitures and impairments, net
Derivative Instruments, Gain (Loss) [Line Items]
Gain/(loss) reclassified from Accumulated OCI into income	$ 0	26	$ 0	26
Trans Mountain and Trans Mountain Expansion Project | Foreign currency contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gain/(loss) reclassified from Accumulated OCI into income		$ 26		$ 26