Discontinued Operations and Assets Held for Sale (Carrying Amounts of Assets and Liabilities Classified as Associated with Discontinued Operations on Consolidated Balance Sheets) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Cash restricted for discontinued operations	$ 200	$ 380
Accounts receivable	37	39
Other current assets	7	7
Oil and gas property and equipment, based on successful efforts accounting, net	593	751
Other property and equipment, net	11	11
Goodwill	88	88
Other long-term assets	74	81
Total assets associated with discontinued operations	810	977
Accounts payable	20	19
Revenues and royalties payable	39	47
Other current liabilities	94	252
Asset retirement obligations	141	141
Other long-term liabilities	163	185
Total liabilities associated with discontinued operations	457	644
Barnett Shale [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Cash restricted for discontinued operations	25	25
Accounts receivable	36	38
Other current assets	5	5
Oil and gas property and equipment, based on successful efforts accounting, net	593	751
Other property and equipment, net	11	11
Goodwill	88	88
Total assets associated with discontinued operations	733	893
Accounts payable	14	15
Revenues and royalties payable	36	44
Other current liabilities	21	19
Asset retirement obligations	141	141
Other long-term liabilities	15	16
Total liabilities associated with discontinued operations	227	235
Canada [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Cash restricted for discontinued operations	175	355
Accounts receivable	1	1
Other current assets	2	2
Other long-term assets	74	81
Total assets associated with discontinued operations	77	84
Accounts payable	6	4
Revenues and royalties payable	3	3
Other current liabilities	73	233
Other long-term liabilities	148	169
Total liabilities associated with discontinued operations	$ 230	$ 409