Equity Investments and Loans (Schedule of Carrying Value Equity Investments) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Feb. 28, 2019
Schedule of Equity Method Investments [Line Items]
Carrying Value	$ 3,136	$ 2,961
Dakota Access, LLC and Energy Transfer Crude Oil Company, LLC (Bakken Pipeline)
Schedule of Equity Method Investments [Line Items]
Percentage Ownership	25.00%
Carrying Value	$ 595	592
Bayou Bridge Pipeline, LLC (Bayou Bridge)
Schedule of Equity Method Investments [Line Items]
Percentage Ownership	40.00%
Carrying Value	$ 296	294
DCP Sand Hills Pipeline, LLC (Sand Hills)
Schedule of Equity Method Investments [Line Items]
Percentage Ownership	33.34%
Carrying Value	$ 598	595
DCP Southern Hills Pipeline, LLC (Southern Hills)
Schedule of Equity Method Investments [Line Items]
Percentage Ownership	33.34%
Carrying Value	$ 218	215
Explorer Pipeline Company (Explorer)
Schedule of Equity Method Investments [Line Items]
Percentage Ownership	21.94%
Carrying Value	$ 102	105
Gray Oak Pipeline, LLC
Schedule of Equity Method Investments [Line Items]
Percentage Ownership	65.00%		65.00%
Carrying Value	$ 799	759
Liberty Pipeline LLC (Liberty)
Schedule of Equity Method Investments [Line Items]
Percentage Ownership	50.00%
Carrying Value	$ 103	0
Paradigm Pipeline LLC (Paradigm)
Schedule of Equity Method Investments [Line Items]
Percentage Ownership	50.00%
Carrying Value	$ 143	143
Phillips 66 Partners Terminal LLC (Phillips 66 Partners Terminal)
Schedule of Equity Method Investments [Line Items]
Percentage Ownership	70.00%
Carrying Value	$ 67	70
South Texas Gateway Terminal LLC (South Texas Gateway Terminal)
Schedule of Equity Method Investments [Line Items]
Percentage Ownership	25.00%
Carrying Value	$ 102	74
STACK Pipeline LLC (STACK)
Schedule of Equity Method Investments [Line Items]
Percentage Ownership	50.00%
Carrying Value	$ 113	$ 114