CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Current Assets
Cash and cash equivalents	$ 0	$ 0
Accounts receivable, net	274.3	397.4
Fair value of derivative contracts	187.2	273.7
Inventories, at lower of average cost or market
Gas, oil and NGL	14.0	16.2
Materials and supplies	94.9	87.6
Prepaid expenses and other	49.4	43.7
Total Current Assets	619.8	818.6
Property, Plant and Equipment (successful efforts method for gas and oil properties)
Proved properties	9,882.4	8,172.4
Unproved properties	983.4	326.8
Midstream field services property	1,605.2	1,463.6
Marketing and other	56.3	49.8
Total Property, Plant and Equipment	12,527.3	10,012.6
Less Accumulated Depreciation, Depletion and Amortization
Exploration and production	3,977.6	3,339.2
Midstream field services	342.9	297.5
Marketing and other	16.9	14.6
Total Accumulated Depreciation, Depletion and Amortization	4,337.4	3,651.3
Net Property, Plant and Equipment	8,189.9	6,361.3
Investment in unconsolidated affiliates	41.7	42.2
Goodwill	59.5	59.5
Fair value of derivative contracts	35.2	123.5
Other noncurrent assets	50.0	37.6
TOTAL ASSETS	8,996.1	7,442.7
Current Liabilities
Checks outstanding in excess of cash balances	27.5	29.4
Accounts payable and accrued expenses	464.6	457.3
Production and property taxes	56.3	40.0
Interest payable	23.7	24.4
Fair value of derivative contracts	2.7	1.3
Deferred income taxes	41.9	85.4
Total Current Liabilities	616.7	637.8
Long-term debt	3,180.7	1,679.4
Deferred income taxes	1,505.8	1,484.7
Asset retirement obligations	176.6	163.9
Fair value of derivative contracts	4.1	0
Other long-term liabilities	135.2	124.8
Commitments and contingencies
EQUITY
Common stock - par value $0.01 per share; 500.0 million shares authorized; 178.5 million and 177.2 million shares issued, respectively	1.8	1.8
Treasury stock - 0.4 million and 0.4 million shares, respectively	(11.6)	(13.1)
Additional paid-in capital	455.8	431.4
Retained earnings	2,805.6	2,673.5
Accumulated other comprehensive income	77.4	207.9
Total Common Shareholders' Equity	3,329.0	3,301.5
Noncontrolling interest	48.0	50.6
Total Equity	3,377.0	3,352.1
TOTAL LIABILITIES AND EQUITY	$ 8,996.1	$ 7,442.7