CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
OPERATING ACTIVITIES
Net income (loss)	$ (863.8)	$ (55.6)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization	240.0	195.4
Deferred income taxes	(446.7)	(4.8)
Impairment	1,182.4	20.0
Share-based compensation	8.0	9.1
Amortization of debt issuance costs and discounts	1.6	1.9
Net (gain) loss from asset sales	(0.5)	30.5
Unrealized (gains) losses on marketable securities	(0.2)	0.0
Unrealized (gains) losses on derivative contracts	13.5	23.5
Changes in operating assets and liabilities	(52.6)	(492.7)
Net Cash Provided by (Used in) Operating Activities	81.7	(272.7)
INVESTING ACTIVITIES
Property acquisitions	(14.8)	0.0
Property, plant and equipment, including dry exploratory well expense	(185.8)	(342.1)
Proceeds from disposition of assets	22.9	1.6
Net Cash Provided by (Used in) Investing Activities	(177.7)	(340.5)
FINANCING ACTIVITIES
Checks outstanding in excess of cash balances	(29.8)	(38.9)
Treasury stock repurchases	(2.9)	(1.9)
Other capital contributions	0.2	(0.4)
Dividends paid	0.0	(3.5)
Proceeds from issuance of common stock, net	368.6	0.0
Excess tax (provision) benefit on share-based compensation	0.2	(1.8)
Net Cash Provided by (Used in) Financing Activities	336.3	(46.5)
Change in cash and cash equivalents	240.3	(659.7)
Beginning cash and cash equivalents	376.1	1,160.1
Ending cash and cash equivalents	616.4	500.4
Supplemental Disclosures:
Cash paid for interest, net of capitalized interest	37.8	37.6
Cash paid for income taxes	32.0	509.8
Non-cash Investing Activities
Change in capital expenditure accruals and other non-cash adjustments	$ (22.6)	$ (59.2)