CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
REVENUES
Oil sales	$ 769.1	$ 834.2	$ 1,368.5
Gas sales	417.1	468.5	776.4
NGL sales	83.5	80.0	223.3
Other revenues	6.2	15.1	11.1
Purchased oil, gas and NGL sales	101.2	620.8	913.9
Total Revenues	1,377.1	2,018.6	3,293.2
OPERATING EXPENSES
Purchased oil, gas and NGL expense	105.5	626.8	910.1
Lease operating expense	224.7	238.8	240.1
Oil, gas and NGL transportation and other handling costs	289.2	291.3	277.6
Gathering and other expense	5.0	5.8	6.7
General and administrative	198.4	181.1	204.4
Production and property taxes	94.8	117.6	205.2
Depreciation, depletion and amortization	871.1	881.1	994.7
Exploration expenses	1.7	2.7	9.9
Impairment	1,194.3	55.6	1,143.2
Total Operating Expenses	2,984.7	2,400.8	3,991.9
Net gain (loss) from asset sales	5.0	4.6	(148.6)
OPERATING INCOME (LOSS)	(1,602.6)	(377.6)	(847.3)
Realized and unrealized gains (losses) on derivative contracts (Note 7)	(233.0)	277.2	363.3
Interest and other income	25.6	3.0	12.8
Income from unconsolidated affiliates	0.0	0.0	0.3
Loss from early extinguishment of debt	0.0	0.0	(2.0)
Interest expense	(143.2)	(145.6)	(169.1)
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAXES	(1,953.2)	(243.0)	(642.0)
Income tax (provision) benefit	708.2	93.6	232.5
NET INCOME FROM CONTINUING OPERATIONS	(1,245.0)	(149.4)	(409.5)
Net income from discontinued operations, net of income tax	0.0	0.0	1,193.9
NET INCOME (LOSS)	$ (1,245.0)	$ (149.4)	$ 784.4
Earnings (Loss) Per Common Share
Basic total	$ (5.62)	$ (0.85)	$ 4.36
Diluted total	$ (5.62)	$ (0.85)	$ 4.36
Weighted-average common shares outstanding
Used in basic calculation	221.7	176.6	179.8
Used in diluted calculation	221.7	176.6	179.8
Dividends per common share	$ 0.00	$ 0.08	$ 0.08
Continuing Operations [Member]
Earnings (Loss) Per Common Share
Basic total	(5.62)	(0.85)	(2.28)
Diluted total	(5.62)	(0.85)	(2.28)
Discontinued Operations [Member]
Earnings (Loss) Per Common Share
Basic total	0.00	0.00	6.64
Diluted total	$ 0.00	$ 0.00	$ 6.64