Accounting For Certain Long-Lived Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Impaired Long-Lived Assets Held and Used [Line Items]
Proved oil and gas properties carrying amount	$ 139	$ 370
Proved oil and gas properties, other property, plant and equipment, and other assets written down to fair value	18	146
Pretax impairment chages for proved oil and gas properties, other property, plant and equipment and other assets	121	224
Amortization and Impairments of Unproved Oil and Gas Property Including Amortization of Capitalized Interest	$ 173	$ 211	$ 291