Equity Investments and Loans (Schedule of Equity Investments) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Feb. 28, 2019	Jan. 31, 2019	Dec. 31, 2018	Apr. 30, 2018	Oct. 31, 2017
Schedule of Equity Method Investments [Line Items]
Carrying Value	$ 2,961			$ 2,448
Bakken Pipeline
Schedule of Equity Method Investments [Line Items]
Percentage Ownership	25.00%					25.00%
Carrying Value	$ 592			608
Bayou Bridge Pipeline, LLC (Bayou Bridge)
Schedule of Equity Method Investments [Line Items]
Percentage Ownership	40.00%
Carrying Value	$ 294			277
DCP Sand Hills Pipeline, LLC (Sand Hills)
Schedule of Equity Method Investments [Line Items]
Percentage Ownership	33.34%
Carrying Value	$ 595			601
DCP Southern Hills Pipeline, LLC (Southern Hills)
Schedule of Equity Method Investments [Line Items]
Percentage Ownership	33.34%
Carrying Value	$ 215			206
Explorer Pipeline Company (Explorer)
Schedule of Equity Method Investments [Line Items]
Percentage Ownership	21.94%
Carrying Value	$ 105			$ 115
Gray Oak Pipeline, LLC
Schedule of Equity Method Investments [Line Items]
Percentage Ownership	65.00%	75.00%	65.00%	75.00%
Carrying Value	$ 759			$ 288
Paradigm Pipeline LLC (Paradigm)
Schedule of Equity Method Investments [Line Items]
Percentage Ownership	50.00%
Carrying Value	$ 143			145
Phillips 66 Partners Terminal LLC (Phillips 66 Partners Terminal)
Schedule of Equity Method Investments [Line Items]
Percentage Ownership	70.00%
Carrying Value	$ 70			71
South Texas Gateway Terminal LLC (South Texas Gateway Terminal)
Schedule of Equity Method Investments [Line Items]
Percentage Ownership	25.00%				25.00%
Carrying Value	$ 74			20
STACK Pipeline LLC (STACK)
Schedule of Equity Method Investments [Line Items]
Percentage Ownership	50.00%
Carrying Value	$ 114			$ 117