Quarterly Results (Unaudited) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Results (Unaudited) [Abstract]
Operating revenues	$ 962	$ 928	$ 1,035	$ 1,113	$ 907	$ 868	$ 862	$ 734	$ 4,038	$ 3,371	$ 2,730
Operating income (loss)	285	286	367	435	317	309	325	252	1,373	1,204	(1,101)
Net income (loss)	$ 312	$ 211	$ 207	$ 194	$ 144	$ 186	$ 246	$ 128	$ 924	$ 704	$ (707)
Earnings per share attributable to Southwestern Energy stockholders - Basic	$ 0.89	$ 0.60	$ 0.59	$ 0.55	$ 0.41	$ 0.53	$ 0.70	$ 0.36	$ 2.63	$ 2.01	$ (2.03)
Earnings per share attributable to Southwestern Energy stockholders - Diluted	$ 0.88	$ 0.60	$ 0.59	$ 0.55	$ 0.41	$ 0.53	$ 0.70	$ 0.36	$ 2.62	$ 2.00	$ (2.03)