Non-Mineral Leases - Balance Sheet (Details) - USD ($)		Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Accumulated depreciation, depletion and amortization		$ (66,969,000,000)		$ (64,899,000,000)
Property, Plant and Equipment, Net		45,942,000,000		45,698,000,000
Debt, Current		113,000,000		112,000,000
Long-term Debt and Capital Lease Obligations		14,832,000,000		14,856,000,000
Finance Lease, Liability Total		759,000,000
Other Assets, Noncurrent		2,303,000,000		1,344,000,000
Other Liabilities, Current		1,402,000,000		1,259,000,000
Deferred Credits and Other Liabilities		1,838,000,000		1,192,000,000
Operating Lease, Liability		967,000,000
Scenario, Previously Reported [Member]
Property, Plant and Equipment, Gross				1,044,000,000
Accumulated depreciation, depletion and amortization				(550,000,000)
Property, Plant and Equipment, Net				494,000,000
Finance Lease, Liability, Current				79,000,000
Finance Lease, Liability, Noncurrent				698,000,000
Finance Lease, Liability Total				$ 777,000,000
Accounting Standards Update 2016-02 (Topic 842) [Member]
Property, Plant and Equipment, Gross		1,044,000,000
Accumulated depreciation, depletion and amortization		(579,000,000)
Property, Plant and Equipment, Net	[1]	465,000,000
Debt, Current	[2]	80,000,000
Long-term Debt and Capital Lease Obligations	[2]	679,000,000
Finance Lease, Liability Total		759,000,000
Other Assets, Noncurrent		981,000,000
Other Liabilities, Current		282,000,000
Deferred Credits and Other Liabilities		685,000,000
Operating Lease, Liability		$ 967,000,000
Accounting Standards Update 2016-02 (Topic 842) [Member] | Restatement Adjustment [Member]
Operating Lease, Right-of-Use Asset			$ 998,000,000
Operating Lease, Liability			$ 998,000,000

[1] *Includes proportionately consolidated finance lease assets (net of accumulated depreciation, depletion and amortization) of $398 million.

[2] *Short-term debt and long-term debt include proportionately consolidated finance lease liabilities of $54 million and $622 million, respectively.