CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Millions, except Share data	Sep. 30, 2011	Dec. 31, 2010
CONDENSED CONSOLIDATED BALANCE SHEETS
Gas and oil properties, using the full cost method, costs excluded from amortization	$ 870.2	$ 712.1
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	1,250,000,000	1,250,000,000
Common stock, shares issued	348,264,799	347,733,839
Treasury stock, shares	125,984	156,636