CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
OPERATING ACTIVITIES
Net income (loss)	$ (149.4)	$ 784.4	$ 159.4
Net income attributable to noncontrolling interest	0.0	21.6	12.0
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, Depletion and Amortization Including Discontinued Operations	881.1	1,040.6	1,016.0
Deferred income taxes	25.3	(84.1)	66.1
Impairment	55.6	1,143.2	93.0
Equity-based compensation	34.7	27.2	27.1
Other Operating Activities, Curtailment Loss	11.2	0.0	0.0
Amortization of debt issuance costs and discounts	6.2	6.7	6.4
Net gain from asset sales	(4.6)	(1,644.8)	(103.0)
Income from unconsolidated affiliates	0.0	(5.2)	(5.8)
Distributions from unconsolidated affiliates and other	0.0	9.4	7.9
Non-cash loss on early extinguishment of debt	0.0	4.4	0.0
Marketable Securities, Unrealized Gain (Loss)	0.2	0.0	0.0
Unrealized loss (gain) on derivative contracts	$ 183.7	$ (374.4)	$ 88.7
Changes in operating assets and liabilities
Accounts receivable	$ 165.5	$ (160.5)	$ 3.2
Inventories	15.5	(20.2)	2.6
Prepaid expenses	16.7	(7.3)	14.0
Accounts payable and accrued expenses	(71.3)	320.1	(179.7)
Federal income taxes	(619.4)	494.1	(27.4)
Other	(69.7)	(12.7)	11.2
Net Cash Provided by Operating Activities	481.3	1,542.5	1,191.7
INVESTING ACTIVITIES
Property acquisitions	(98.3)	(960.5)	(40.9)
Property, plant and equipment, including dry exploratory well expense	(1,141.1)	(1,765.9)	(1,561.7)
Proceeds from Sale of Oil and Gas Property and Equipment	21.8	3,296.6	211.1
Acquisition deposit held in escrow	0.0	50.0	(50.0)
Other investments	0.0	(42.0)	0.0
Net Cash Provided by (Used in) Investing Activities	(1,217.6)	578.2	(1,441.5)
FINANCING ACTIVITIES
Checks outstanding in excess of cash balances	(24.9)	(54.4)	69.3
Long-term debt issued	0.0	300.0	0.0
Long-term debt issuance costs paid	(2.6)	(9.3)	(3.2)
Long-term debt repaid	0.0	(600.0)	0.0
Proceeds from credit facility	0.0	5,455.0	3,085.0
Repayments of credit facility	0.0	(5,935.0)	(3,295.0)
Common stock repurchased and retired	0.0	(99.7)	0.0
Treasury stock repurchased	(2.7)	(6.2)	(9.3)
Other capital contributions	(0.2)	6.0	7.0
Dividends paid	(14.1)	(14.6)	(14.3)
Excess Tax Benefit (provision) from Share-based Compensation, Financing Activities	(3.2)	(0.5)	0.0
Net proceeds from the issuance of common units	0.0	0.0	449.6
Distribution to noncontrolling interest	0.0	(31.9)	(9.3)
Net Cash Provided by (Used in) Financing Activities	(47.7)	(990.6)	279.8
Change in cash and cash equivalents	(784.0)	1,130.1	30.0
Beginning cash and cash equivalents	1,160.1	30.0	0.0
Ending cash and cash equivalents	$ 376.1	$ 1,160.1	$ 30.0