Fair Value Measurement - FV Hierarchy (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in debt securities	$ 459	$ 241
Commodity derivative asset, gross	399	322
Commodity derivative liability, gross	359	311
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in Equity Securities	420	2,111
Investments in debt securities	459	241
Commodity derivative asset, gross	399	322
Total assets	1,278	2,674
Commodity derivative liability, gross	359	311
Total liabilities	359	311
Fair Value, Measurements, Recurring [Member] \| Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in Equity Securities	420	2,111
Investments in debt securities	21	25
Commodity derivative asset, gross	196	172
Total assets	637	2,308
Commodity derivative liability, gross	244	174
Total liabilities	244	174
Fair Value, Measurements, Recurring [Member] \| Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in Equity Securities	0	0
Investments in debt securities	438	216
Commodity derivative asset, gross	168	114
Total assets	606	330
Commodity derivative liability, gross	102	115
Total liabilities	102	115
Fair Value, Measurements, Recurring [Member] \| Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in Equity Securities	0	0
Investments in debt securities		0
Commodity derivative asset, gross	35	36
Total assets	35	36
Commodity derivative liability, gross	13	22
Total liabilities	$ 13	$ 22

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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