Financial Instruments - Narrative (Details) gal in Thousands, MBbls in Thousands, BTU in Thousands, $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($) Contract	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) BTU Contract gal MBbls	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) BTU MBbls
Credit Derivatives [Line Items]
Number of contracts that are designated as accounting hedges | Contract	0		0
Derivative (loss) gain on oil and natural gas financial derivative instruments	$ 434	$ 381	$ 458	$ (44)
Interest rate derivative instruments | Derivatives not designated as accounting hedges
Credit Derivatives [Line Items]
Monetary notional amount	600		600
Net liability related to interest rate derivatives (less than $1 million)	2		2
Net asset related to interest rate derivatives					$ 3
Interest expense (income) related to the change in fair market value and cash settlements of interest rate derivative instruments	$ 2	$ (2)	$ 7	$ 2
Oil derivatives | Fixed Price Swaps | Derivatives not designated as accounting hedges
Credit Derivatives [Line Items]
Nonmonetary notional amount (in MBbls or gal) | MBbls			29,000		37,000
Natural gas derivatives | Fixed Price Swaps | Derivatives not designated as accounting hedges
Credit Derivatives [Line Items]
Nonmonetary notional amount (in Btu) | BTU			23,000		69,000
Propane derivatives | Fixed Price Swaps | Derivatives not designated as accounting hedges
Credit Derivatives [Line Items]
Nonmonetary notional amount (in MBbls or gal) | gal			27,000