CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Current Assets
Cash and cash equivalents	$ 0	$ 0
Accounts receivable, net	303.5	397.4
Fair value of derivative contracts	333.8	273.7
Inventories, at lower of average cost or market
Gas, oil and NGL	10.9	16.2
Materials and supplies	86.6	87.6
Prepaid expenses and other	40.6	43.7
Total Current Assets	775.4	818.6
Property, Plant and Equipment (successful efforts method for gas and oil properties)
Proved properties	8,468.3	8,172.4
Unproved properties, not being depleted	316.0	326.8
Midstream field services	1,510.8	1,463.6
Marketing and other	51.6	49.8
Total Property, Plant and Equipment	10,346.7	10,012.6
Less Accumulated Depreciation, Depletion and Amortization
Exploration and production	3,519.9	3,339.2
Midstream field services	312.2	297.5
Marketing and other	15.5	14.6
Total Accumulated Depreciation, Depletion and Amortization	3,847.6	3,651.3
Net Property, Plant and Equipment	6,499.1	6,361.3
Investment in unconsolidated affiliates	42.6	42.2
Goodwill	59.5	59.5
Fair value of derivative contracts	115.6	123.5
Other noncurrent assets	40.9	37.6
TOTAL ASSETS	7,533.1	7,442.7
Current Liabilities
Checks outstanding in excess of cash balances	58.6	29.4
Accounts payable and accrued expenses	380.7	457.3
Production and property taxes	43.5	40.0
Interest payable	8.9	24.4
Fair value of derivative contracts	0	1.3
Deferred income taxes	57.6	85.4
Total Current Liabilities	549.3	637.8
Long-term debt	1,673.5	1,679.4
Deferred income taxes	1,554.5	1,484.7
Asset retirement obligations	167.7	163.9
Fair value of derivative contracts	0.1	0
Other long-term liabilities	130.3	124.8
Commitments and contingencies
EQUITY
Common stock - par value $0.01 per share; 500.0 million shares authorized 178.4 million and 177.2 million shares issued, respectively	1.8	1.8
Treasury stock - 0.7 million and 0.4 million shares, respectively	(23.4)	(13.1)
Additional paid-in capital	442.6	431.4
Retained earnings	2,825.1	2,673.5
Accumulated other comprehensive income	161.9	207.9
Total Common Shareholders' Equity	3,408.0	3,301.5
Noncontrolling interest	49.7	50.6
Total Equity	3,457.7	3,352.1
TOTAL LIABILITIES AND EQUITY	$ 7,533.1	$ 7,442.7