Fair Value Measurement - Nonrecurring (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value - Net PP&E (held for use)	$ 87	[1]	$ 117	[1]
Before-Tax Loss - Net PP&E (held for use)	756		488
Fair Value - Net PP&E (unproved property)	39	[1]
Before-Tax Loss - Net PP&E (unproved propery)	158
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value - Net PP&E (held for use)	87		117
Fair Value - Net PP&E (unproved property)	$ 39

[1] *Represents the fair value at the time of the impairment.