Derivative and Hedging Activities - Natural Gas and Oil Sales Table (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) on undesignated oil and natural gas derivatives	$ 0	$ 33	$ 10	$ 51
Total oil, natural gas and NGL sales	728	1,704	1,813	3,471
Oil And Gas Exploration And Production [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Oil, natural gas and NGL sales	776	1,917	1,700	4,065
Gains (losses) on undesignated oil and natural gas derivatives	(43)	(210)	135	(574)
Losses on terminated cash flow hedges	$ (5)	$ (3)	$ (22)	$ (20)