CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Net income (loss)	$ 245,631		$ (405,132)		$ 373,146		$ (297,428)
Change in derivatives:
Settlements	(27,801)	[1]	(117,944)	[1]	(74,974)	[1]	(215,886)	[1]
Ineffectiveness	1,219	[2]	1,620	[2]	438	[2]	(1,537)	[2]
Change in fair value of derivative instruments	67,572	[3]	(36,481)	[3]	22,091	[3]	130,453	[3]
Total change in derivatives	40,990		(152,805)		(52,445)		(86,970)
Change in value of pension and other postretirement liabilities:
Amortization of prior service cost included in net periodic pension cost	267	[4]	254	[4]	534	[4]	508	[4]
Change in currency translation adjustment	(1,418)		(516)		(2,447)		(35)
Comprehensive income (loss)	$ 285,470		$ (558,199)		$ 318,788		$ (383,925)

[1] Net of ($18.5), ($76.7), ($50.0) and ($140.4) million in taxes for the three months ended June 30, 2013 and 2012, and six months ended June 30, 2013 and 2012, respectively.

[2] Net of $0.8, $1.1, $0.3 and ($1.0) million in taxes for the three months ended June 30, 2013 and 2012, and six months ended June 30, 2013 and 2012, respectively.

[3] Net of $45.0, ($23.7), $14.7, and $84.8 million in taxes for the three months ended June 30, 2013 and 2012, and six months ended June 30, 2013 and 2012, respectively.

[4] Net of $0.2, $0.1, $0.4, and $0.3 million in taxes for the three months ended June 30, 2013 and 2012, and six months ended June 30, 2013 and 2012, respectively.