CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Current Assets
Cash and cash equivalents	$ 3.9	$ 11.9
Accounts receivable, net	586.5	408.5
Fair value of derivative contracts	0	0.2
Gas, oil and NGL inventories at lower of average cost or market	7.8	13.4
Deferred income taxes	50.4	30.6
Prepaid expenses and other	61.8	54.4
Total Current Assets	710.4	519.0
Property, Plant and Equipment (successful efforts method for gas and oil properties)
Proved properties	12,401.4	11,571.4
Unproved properties	1,102.5	665.1
Midstream field services	1,719.2	1,698.1
Marketing and other	89.4	85.5
Material and supplies	64.8	59.0
Total Property, Plant and Equipment	15,377.3	14,079.1
Less Accumulated Depreciation, Depletion and Amortization
Exploration and production	5,146.5	4,930.9
Midstream field services	425.0	409.7
Marketing and other	24.2	22.1
Total Accumulated Depreciation, Depletion and Amortization	5,595.7	5,362.7
Net Property, Plant and Equipment	9,781.6	8,716.4
Investment in unconsolidated affiliates	38.5	39.0
Fair value of derivative contracts	3.9	1.0
Restricted cash	0	50.0
Other noncurrent assets	45.2	51.4
TOTAL ASSETS	10,579.6	9,376.8
Current Liabilities
Checks outstanding in excess of cash balances	78.4	90.9
Accounts payable and accrued expenses	581.0	434.9
Production and property taxes	62.3	51.8
Interest payable	34.2	37.2
Fair value of derivative contracts	71.8	26.7
Total Current Liabilities	827.7	641.5
Long-term debt	3,919.2	2,997.5
Deferred income taxes	1,601.7	1,560.6
Asset retirement obligations	204.3	191.8
Fair value of derivative contracts	2.9	0
Other long-term liabilities	108.1	108.6
Commitments and contingencies
EQUITY
Common stock - par value $0.01 per share; 500.0 million shares authorized; 180.7 million and 179.7 million shares issued, respectively	1.8	1.8
Treasury stock - 0.6 million and 0.4 million shares, respectively	(20.9)	(14.9)
Additional paid-in capital	508.1	498.4
Retained earnings	2,953.8	2,917.8
Accumulated other comprehensive income	(25.5)	(26.5)
Total Common Shareholders' Equity	3,417.3	3,376.6
Noncontrolling interest	498.4	500.2
Total Equity	3,915.7	3,876.8
TOTAL LIABILITIES AND EQUITY	$ 10,579.6	$ 9,376.8