Supplemental Oil and Gas Disclosures (Schedule of Prices Used for Standardized Measure of Discounted Future Cash Flows Relating to Proved Reserves Disclosure) (Details)	12 Months Ended
Dec. 31, 2017 $ / bbl $ / MMBTU	Dec. 31, 2016 $ / bbl $ / MMBTU	Dec. 31, 2015 $ / bbl $ / MMBTU
Natural Gas [Member]
Reserve Quantities [Line Items]
Full cost ceiling test, price \| $ / MMBTU	2.98	2.48	2.59
Oil [Member]
Reserve Quantities [Line Items]
Full cost ceiling test, price	47.79	39.25	46.79
NGL [Member]
Reserve Quantities [Line Items]
Full cost ceiling test, price	14.41	6.74	6.82

Price used in the full cost ceiling test. Prior to the fourth quarter of 2009, this price was the quoted market price as of the balance sheet date (if the quoted price at the balance sheet date resulted in an impairment, management could previously use a more favorable quoted market price at a day subsequent to the balance sheet date but prior to the auditor's report on the affected financial statements). For all periods including and subsequent to the fourth quarter of 2009, this price is an average of the prices for the first-day-of-the-month during the previous 12 months.

No definition available.

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Namespace Prefix:	swn_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	duration