Fair Value Measurements Fair Value Measurements (Nonrecurring Fair Value Measurements) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended				3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014 Hugoton field [Member]	Mar. 31, 2014 Pioneer Alaska [Member]	Sep. 30, 2014 Barnett Shale Field [Member]	Sep. 30, 2014 Discontinued Operations [Member]	Sep. 30, 2013 Discontinued Operations [Member]	Sep. 30, 2014 Discontinued Operations [Member]	Sep. 30, 2013 Discontinued Operations [Member]	Sep. 30, 2014 Discontinued Operations [Member] Hugoton field [Member]	Sep. 30, 2014 Discontinued Operations [Member] Hugoton field [Member]	Sep. 30, 2014 Discontinued Operations [Member] Pioneer Alaska [Member]	Sep. 30, 2014 Discontinued Operations [Member] Pioneer Alaska [Member]	Sep. 30, 2014 Discontinued Operations [Member] Barnett Shale Field [Member]	Sep. 30, 2014 Discontinued Operations [Member] Barnett Shale Field [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Inventory Write-down	$ 3	$ 6
Fair Value of Asset Group			328	253	149
Impairment of oil and gas properties						$ (80)	$ 0	$ (305)	$ 0	$ (34)	$ (34)	$ 0	$ (97)	$ (46)	$ (174)