CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Natural gas and oil properties, using the full cost method, costs excluded from amortization	$ 3,505	$ 3,727
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	1,250,000,000	1,250,000,000
Common stock, shares issued	389,673,678	390,138,549
Common stock, shares declared as stock dividend	3,024,737
Treasury stock, shares	31,269	47,149
Series B Preferred Stock [Member]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, dividend rate	6.25%	6.25%
Liquidation preference per share	$ 1,000	$ 1,000
Preferred stock, shares issued	1,725,000	1,725,000
Preferred stock, shares outstanding	1,725,000	1,725,000