Derivative Financial Instruments (Oil Derivative Contracts Volume And Weighted Average Price) (Details)	3 Months Ended				12 Months Ended
	Dec. 31, 2011 bbl Mmbtu	Sep. 30, 2011 bbl Mmbtu	Jun. 30, 2011 bbl Mmbtu	Mar. 31, 2011 bbl Mmbtu	Dec. 31, 2011 Mmbtu bbl
2011 - Swap Contracts [Member]
Volume	750,000,000,000	750,000,000,000			750,000,000,000
NYMEX price	77.25	77.25			77.25
2011 - Collar Contracts [Member]
Volume	2,000,000,000,000	2,000,000,000,000			2,000,000,000,000
2011 - Collar Contracts [Member] | Ceiling [Member]
NYMEX price	170.00	170.00			170.00
2011 - Collar Contracts [Member] | Floor [Member]
NYMEX price	115.00	115.00			115.00
2011 - Collar Contracts With Short Puts [Member]
Volume	32,000,000,000,000	32,000,000,000,000			32,000,000,000,000
2011 - Collar Contracts With Short Puts [Member] | Ceiling [Member]
NYMEX price	99.33	99.33			99.33
2011 - Collar Contracts With Short Puts [Member] | Floor [Member]
NYMEX price	73.75	73.75			73.75
2011 - Collar Contracts With Short Puts [Member] | Short Put [Member]
NYMEX price	59.31	59.31			59.31
2012 - Swap Contracts [Member]
Volume	3,000,000,000,000	3,000,000,000,000	3,000,000,000,000	3,000,000,000,000	3,000,000,000,000
NYMEX price	79.32	79.32	79.32	79.32	79.32
2012 - Collar Contracts [Member]
Volume	2,000,000,000,000	2,000,000,000,000	2,000,000,000,000	2,000,000,000,000	2,000,000,000,000
2012 - Collar Contracts [Member] | Ceiling [Member]
NYMEX price	127.00	127.00	127.00	127.00	127.00
2012 - Collar Contracts [Member] | Floor [Member]
NYMEX price	90.00	90.00	90.00	90.00	90.00
2012 - Collar Contracts With Short Puts [Member]
Volume	36,000,000,000,000	36,000,000,000,000	36,000,000,000,000	36,000,000,000,000	36,000,000,000,000
2012 - Collar Contracts With Short Puts [Member] | Ceiling [Member]
NYMEX price	117.99	117.99	117.99	117.99	117.99
2012 - Collar Contracts With Short Puts [Member] | Floor [Member]
NYMEX price	80.42	80.42	80.42	80.42	80.42
2012 - Collar Contracts With Short Puts [Member] | Short Put [Member]
NYMEX price	65.00	65.00	65.00	65.00	65.00
2013 - Swap Contracts [Member]
Volume	3,000,000,000,000	3,000,000,000,000	3,000,000,000,000	3,000,000,000,000	3,000,000,000,000
NYMEX price	81.02	81.02	81.02	81.02	81.02
2013 - Collar Contracts With Short Puts [Member]
Volume	21,250,000,000,000	21,250,000,000,000	21,250,000,000,000	21,250,000,000,000	21,250,000,000,000
2013 - Collar Contracts With Short Puts [Member] | Ceiling [Member]
NYMEX price	117.38	117.38	117.38	117.38	117.38
2013 - Collar Contracts With Short Puts [Member] | Floor [Member]
NYMEX price	80.18	80.18	80.18	80.18	80.18
2013 - Collar Contracts With Short Puts [Member] | Short Put [Member]
NYMEX price	65.18	65.18	65.18	65.18	65.18
2014 - Collar Contracts With Short Puts [Member]
Volume	12,000,000,000,000	12,000,000,000,000	12,000,000,000,000	12,000,000,000,000	12,000,000,000,000
2014 - Collar Contracts With Short Puts [Member] | Ceiling [Member]
NYMEX price	128.16	128.16	128.16	128.16	128.16
2014 - Collar Contracts With Short Puts [Member] | Floor [Member]
NYMEX price	87.92	87.92	87.92	87.92	87.92
2014 - Collar Contracts With Short Puts [Member] | Short Put [Member]
NYMEX price	72.92	72.92	72.92	72.92	72.92