Fair Value Measurements (Narrative) (Details) $ in Millions	Mar. 31, 2020 USD ($) d	Dec. 31, 2019 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill	$ 1,425	$ 3,270
DCP Partners | Fair Value, Nonrecurring | Trading Period | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment, measurement input | d	15
Refining
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill	$ 0	$ 1,845