Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities:
Interest paid (net of amounts capitalized)	$ 269	$ 270	$ 379
Income taxes paid to taxing authorities	73	287	391
Asset Retirement Obligation, Period Increase (Decrease)	80	(183)	(202)
Noncash investing and financing activities:
Asset Retirement Obligation, Liabilities Transferred	1,082	82	14
Notes receivable	0	0
Receivable Related To Disposal Of Assets			748
Increase in capital expenditure accrual	288	250	329
Income Tax Examination [Line Items]
Proceeds from Income Tax Refunds	$ 90	$ 37	1
Foreign Tax Authority [Member] | UK Government [Member]
Income Tax Examination [Line Items]
Income Tax Examination, Penalties and Interest Expense			$ 108