CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Natural gas and oil properties, using the full cost method, costs excluded from amortization	$ 3,727	$ 4,646
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	1,250,000,000	1,250,000,000
Common stock, shares issued	390,138,549	354,488,992
Treasury stock, shares	47,149	11,055
Series B Preferred Stock [Member]
Preferred stock, par value	$ 0.01
Preferred stock, shares authorized	10,000,000
Preferred stock, dividend rate	6.25%
Liquidation preference per share	$ 1,000
Preferred stock, shares issued	1,725,000
Preferred stock, shares outstanding	1,725,000