Financial Instruments (Details 2) (USD $) In Millions, unless otherwise specified			9 Months Ended	12 Months Ended			1 Months Ended
	Dec. 31, 2013 item	Dec. 31, 2012 item	Dec. 31, 2012 Derivatives not designated as accounting hedges Interest rate derivative instruments	Dec. 31, 2013 Derivatives not designated as accounting hedges Interest rate derivative instruments	Dec. 31, 2013 Derivatives not designated as accounting hedges Oil derivatives Oil and natural gas swaps, basis swaps and option contracts MMBbls	Dec. 31, 2012 Derivatives not designated as accounting hedges Oil derivatives Oil and natural gas swaps, basis swaps and option contracts MMBbls	Jan. 31, 2014 Derivatives not designated as accounting hedges Oil derivatives Basis Swaps Subsequent event	Dec. 31, 2013 Derivatives not designated as accounting hedges Oil derivatives Basis Swaps 2014 Volumes Subsequent event MBbls	Dec. 31, 2013 Derivatives not designated as accounting hedges Oil derivatives Basis Swaps 2016 Volumes Subsequent event MBbls	Dec. 31, 2013 Derivatives not designated as accounting hedges Brent derivatives Fixed Price Swaps 2014 Volumes Subsequent event MBbls	Dec. 31, 2013 Derivatives not designated as accounting hedges Brent derivatives Fixed Price Swaps 2015 Volumes Subsequent event MBbls	Dec. 31, 2013 Derivatives not designated as accounting hedges Brent derivatives Fixed Price Swaps 2016 Volumes Subsequent event MBbls	Dec. 31, 2013 Derivatives not designated as accounting hedges LLS derivative Fixed Price Swaps 2016 Volumes Subsequent event MBbls	Dec. 31, 2013 Derivatives not designated as accounting hedges Natural gas derivatives Oil and natural gas swaps, basis swaps and option contracts MBTU	Dec. 31, 2012 Derivatives not designated as accounting hedges Natural gas derivatives Oil and natural gas swaps, basis swaps and option contracts MBTU	Dec. 31, 2013 Derivatives not designated as accounting hedges Natural gas derivatives Fixed Price Swaps 2015 Volumes Subsequent event MBTU	Dec. 31, 2013 Derivatives not designated as accounting hedges NGLs derivatives Fixed Price Swaps 2014 Volumes Subsequent event t	Dec. 31, 2013 Derivatives not designated as accounting hedges NGLs derivatives Propane Collars Ceilings 2014 Volumes Subsequent event t	Dec. 31, 2013 Derivatives not designated as accounting hedges NGLs derivatives Propane Collars Floors 2014 Volumes Subsequent event t
Financial Instruments
Nonmonetary notional amount					47	34		1,557	183	160	2,555	4,026	2,562	135	276	4	28	14	14
Monetary notional amount			$ 600
Net asset related to interest rate derivatives				4
Net liability related to interest rate derivatives			2
Interest expense related to the change in fair market value and cash settlements of interest rate derivative instruments			3	(3)
Number of contracts that are designated as accounting hedges	0	0
Cash or other considerations on exchange of derivative instruments							$ 0