Oil and Gas Properties Ceiling Test Impairment (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($) $ / bbl $ / MMBTU	Sep. 30, 2016 USD ($) $ / bbl $ / MMBTU	Jun. 30, 2016 USD ($) $ / bbl $ / MMBTU	Mar. 31, 2016 USD ($) $ / bbl $ / MMBTU	Dec. 31, 2015 USD ($) $ / bbl $ / MMBTU	Sep. 30, 2015 USD ($) $ / bbl $ / MMBTU	Jun. 30, 2015 USD ($) $ / bbl $ / MMBTU	Mar. 31, 2015 USD ($) $ / bbl $ / MMBTU	Dec. 31, 2016 USD ($) $ / bbl $ / MMBTU	Dec. 31, 2015 USD ($) $ / bbl $ / MMBTU
Ceiling Test Impairment [Line Items]
Unweighted average commodity price of oil based on first day of month prices for prior twelve months | $ / bbl	42.82	41.73	43.14	46.23	50.11	59.09	71.56	82.60	42.82	50.11
Unweighted average commodity price of natural gas based on first day of month prices for prior twelve months | $ / MMBTU	2.48	2.28	2.24	2.40	2.59	3.06	3.39	3.88	2.48	2.59
Unamortized Costs Capitalized Less Related Deferred Income Taxes Exceed Ceiling Limitation Expense Gross	$ 0	$ 0	$ 522	$ 506	$ 702	$ 1,889	$ 1,521	$ 788	$ 1,028	$ 4,900
Unamortized Costs Capitalized Less Related Deferred Income Taxes Exceed Ceiling Limitations, Expense	0	0	522	506	651	1,222	958	496	1,028	3,327
UNITED STATES
Ceiling Test Impairment [Line Items]
Unamortized Costs Capitalized Less Related Deferred Income Taxes Exceed Ceiling Limitation Expense Gross	0	0	501	461	656	1,817	1,521	788	962	4,782
Unamortized Costs Capitalized Less Related Deferred Income Taxes Exceed Ceiling Limitations, Expense	0	0	501	461	620	1,193	958	496	962	3,267
China [Member]
Ceiling Test Impairment [Line Items]
Unamortized Costs Capitalized Less Related Deferred Income Taxes Exceed Ceiling Limitation Expense Gross	0	0	21	45	46	72	0	0	66	118
Unamortized Costs Capitalized Less Related Deferred Income Taxes Exceed Ceiling Limitations, Expense	$ 0	$ 0	$ 21	$ 45	$ 31	$ 29	$ 0	$ 0	$ 66	$ 60