Supplementary Oil and Gas Disclosure (Unaudited) - Results of Operations of O&G Producing Activities (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Results Of Operations Income Before Income Taxes Abstract
Revenues	$ 2,369	$ 2,668	$ 2,560
Production costs	322	390	400
Production taxes and other operating expenses	310	488	451
Depreciation, depletion and amortization	903	930	955
Impairment of oil and gas properties			1,488
Income taxes	292	304	(250)
Results of Operations, Oil and Gas Producing Activities Net Income (Excluding Corporate Overhead and Interest Costs), Total	542	556	(484)
Domestic [Member]
Results Of Operations Income Before Income Taxes Abstract
Revenues	2,240	1,777	1,469
Production costs	299	265	292
Production taxes and other operating expenses	279	204	174
Depreciation, depletion and amortization	857	668	683
Impairment of oil and gas properties			1,488
Income taxes	282	224	(410)
Results of Operations, Oil and Gas Producing Activities Net Income (Excluding Corporate Overhead and Interest Costs), Total	523	416	(758)
Malaysia [Member]
Results Of Operations Income Before Income Taxes Abstract
Revenues	90	822	1,005
Production costs	11	117	101
Production taxes and other operating expenses	25	272	259
Depreciation, depletion and amortization	33	244	251
Impairment of oil and gas properties			0
Income taxes	8	72	150
Results of Operations, Oil and Gas Producing Activities Net Income (Excluding Corporate Overhead and Interest Costs), Total	13	117	244
China [Member]
Results Of Operations Income Before Income Taxes Abstract
Revenues	39	69	86
Production costs	12	8	7
Production taxes and other operating expenses	6	12	18
Depreciation, depletion and amortization	13	18	21
Impairment of oil and gas properties			0
Income taxes	2	8	10
Results of Operations, Oil and Gas Producing Activities Net Income (Excluding Corporate Overhead and Interest Costs), Total	$ 6	$ 23	$ 30