Supplemental Information on Oil and Gas Producing Activities (Unaudited) (Detail 4) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Supplemental Information on Oil and Gas Producing Activities (Unaudited)
Weighted average price of equivalent reserves (in dollar per share)	5.02us-gaap_AverageSalesPrices	3.95us-gaap_AverageSalesPrices	2.78us-gaap_AverageSalesPrices
Changes in Standardized Measure of Discounted Future Net Cash Flow
Sales of oil and gas, net of productions costs	$ (1,158)	$ (543)	$ (147)
Net changes in prices and production costs	(184)	1,061	(1,631)
Development costs incurred during the period	564	384	296
Net changes in future development costs	(102)	(181)	(92)
Extensions, discoveries and other additions	5,759	3,441	813
Acquisitions	42	2
Divestitures			(1,277)
Revisions of previous quantity estimates	(828)	(270)	88
Accretion of discount	600us-gaap_AccretionOfDiscount	192us-gaap_AccretionOfDiscount	322us-gaap_AccretionOfDiscount
Net change in income taxes	(2,198)	(1,165)	653
Other changes	630	(12)	106
Net increase (decrease)	3,125	2,909	(869)
Beginning of period	4,510	1,601	2,470
End of period	$ 7,635	$ 4,510	$ 1,601

Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of passage of time.

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The revenues derived from sales of oil or gas in each geographic area during the reporting period divided by the number of barrels of oil produced or thousands of cubic feet of gas produced.

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Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of extensions, discoveries and improved recovery of proved oil and gas reserves.

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Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of change in estimated future development costs.

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Amount of increase in standardized measure of discounted future net cash flow as a result of purchases of minerals in place.

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Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of change in sales and transfer prices and in production (lifting) costs related to future production.

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Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of revisions of estimated quantity of oil and gas in proved reserves.

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Amount of (increase) decrease in standardized measure of discounted future net cash flow as a result of sales and transfers of oil and gas produced.

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Amount of increase (decrease) in standardized measure of discounted future net cash flow as a result of changes from other sources.

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