Property, Plant and Equipment - Components of Property, Plant and Equipment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Land	$ 11		$ 11		$ 11
Building and improvements	40		40		39
Pipeline and equipment	1,225		1,225		1,162
Other	19		19		18
Property, plant and equipment, gross	1,295		1,295		1,230
Accumulated depreciation and amortization	(603)		(603)		(567)
Property plant and equipment excluding construction in progress	692		692		663
Construction in progress	41		41		79
Property, plant and equipment, net	733		733		742
Operating lease cost	0		0
Operating lease, accumulated depreciation	131		131		121
Finance lease, accumulated depreciation	6		6		5
Depreciation and amortization expense	$ 12	$ 11	$ 36	$ 34
Building and Improvements | Minimum
Property Plant And Equipment [Line Items]
Property, plant and equipment, depreciable life			10 years
Building and Improvements | Maximum
Property Plant And Equipment [Line Items]
Property, plant and equipment, depreciable life			40 years
Pipeline and Equipment
Property Plant And Equipment [Line Items]
Operating lease cost			$ 369		366
Finance lease cost			$ 23		$ 23
Pipeline and Equipment | Minimum
Property Plant And Equipment [Line Items]
Property, plant and equipment, depreciable life			10 years
Pipeline and Equipment | Maximum
Property Plant And Equipment [Line Items]
Property, plant and equipment, depreciable life			30 years
Other | Minimum
Property Plant And Equipment [Line Items]
Property, plant and equipment, depreciable life			5 years
Other | Maximum
Property Plant And Equipment [Line Items]
Property, plant and equipment, depreciable life			25 years