Derivative Instruments - Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Gross and net fair values of outstanding derivatives (in millions)
Collateral paid netted against derivative liabilities		$ 1
Collateral received netted against derivative assets		45
Collateral deposited with clearinghouses and brokers		178
Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Collateral deposited with clearinghouses and brokers	$ 36
Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Collateral paid netted against derivative liabilities	359
Other current assets | Oil Collars and Calls
Gross and net fair values of outstanding derivatives (in millions)
Netting, asset	(4)
Total net fair value, asset	213
Other current assets | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Netting, asset	(861)	(2,392)
Total net fair value, asset	74	249
Other current assets | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Netting, asset	0
Total net fair value, asset	14
Long-term receivables and other assets, net | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Netting, asset	(70)	(6)
Total net fair value, asset	12	8
Long-term receivables and other assets, net | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Netting, asset	0
Total net fair value, asset	13
Accrued liabilities | Oil Collars and Calls
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	(3)
Total net fair value, liability	0
Accrued liabilities | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	(861)	(2,392)
Total net fair value, liability	11	66
Accrued liabilities | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	0
Total net fair value, liability	882
Accrued liabilities | Interest Rate Swaps | WES Midstream
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	0
Total net fair value, liability	171
Deferred credits and other liabilities - other | Oil Collars and Calls
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	0
Total net fair value, liability	97
Deferred credits and other liabilities - other | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	(70)	(6)
Total net fair value, liability	2	2
Deferred credits and other liabilities - other | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	0
Total net fair value, liability	879
Deferred credits and other liabilities - other | Warrant
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	0
Total net fair value, liability	168
Level 1 | Other current assets | Oil Collars and Calls
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	0
Level 1 | Other current assets | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	838	2,531
Level 1 | Other current assets | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	0
Level 1 | Long-term receivables and other assets, net | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	70	5
Level 1 | Long-term receivables and other assets, net | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	0
Level 1 | Accrued liabilities | Oil Collars and Calls
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0
Level 1 | Accrued liabilities | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	827	2,357
Level 1 | Accrued liabilities | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0
Level 1 | Accrued liabilities | Interest Rate Swaps | WES Midstream
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0
Level 1 | Deferred credits and other liabilities - other | Oil Collars and Calls
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0
Level 1 | Deferred credits and other liabilities - other | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	71	6
Level 1 | Deferred credits and other liabilities - other | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0
Level 1 | Deferred credits and other liabilities - other | Warrant
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0
Level 2 | Other current assets | Oil Collars and Calls
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	217
Level 2 | Other current assets | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	97	110
Level 2 | Other current assets | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	14
Level 2 | Long-term receivables and other assets, net | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	12	9
Level 2 | Long-term receivables and other assets, net | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	13
Level 2 | Accrued liabilities | Oil Collars and Calls
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	3
Level 2 | Accrued liabilities | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	45	101
Level 2 | Accrued liabilities | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	882
Level 2 | Accrued liabilities | Interest Rate Swaps | WES Midstream
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	171
Level 2 | Deferred credits and other liabilities - other | Oil Collars and Calls
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	97
Level 2 | Deferred credits and other liabilities - other | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	1	2
Level 2 | Deferred credits and other liabilities - other | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	879
Level 2 | Deferred credits and other liabilities - other | Warrant
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	168
Level 3 | Other current assets | Oil Collars and Calls
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	0
Level 3 | Other current assets | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	0	0
Level 3 | Other current assets | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	0
Level 3 | Long-term receivables and other assets, net | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	0	0
Level 3 | Long-term receivables and other assets, net | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	0
Level 3 | Accrued liabilities | Oil Collars and Calls
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0
Level 3 | Accrued liabilities | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0	0
Level 3 | Accrued liabilities | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0
Level 3 | Accrued liabilities | Interest Rate Swaps | WES Midstream
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0
Level 3 | Deferred credits and other liabilities - other | Oil Collars and Calls
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0
Level 3 | Deferred credits and other liabilities - other | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0	$ 0
Level 3 | Deferred credits and other liabilities - other | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0
Level 3 | Deferred credits and other liabilities - other | Warrant
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	$ 0