Acquisition and Divestitures - (Acquisition Narrative) (Details) - USD ($)				1 Months Ended	2 Months Ended	4 Months Ended	12 Months Ended
	Dec. 31, 2021	Sep. 01, 2021	Nov. 13, 2020	Aug. 31, 2020	Dec. 31, 2020	Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Nov. 30, 2021
Business Acquisition [Line Items]
Cash consideration							$ 1,642,000,000	$ 0	$ 0
Long-term debt	$ 5,407,000,000				$ 3,150,000,000	$ 5,407,000,000	5,407,000,000	$ 3,150,000,000
Obligation under transportation agreements	10,456,000,000					10,456,000,000	10,456,000,000
Indigo Agreement
Business Acquisition [Line Items]
Obligation under transportation agreements	36,000,000					36,000,000	36,000,000
Liability for the estimated future payments	17,000,000					17,000,000	17,000,000
Purchase or volume commitments with gathering fresh water and sand
Business Acquisition [Line Items]
Obligation under transportation agreements	74,000,000					74,000,000	$ 74,000,000
Minimum
Business Acquisition [Line Items]
Contractual commitments payments, term (in years)							2 years
Maximum
Business Acquisition [Line Items]
Contractual commitments payments, term (in years)							7 years
Indigo Natural Resources, LLC
Business Acquisition [Line Items]
Cash consideration		$ 373,000,000
Shares of Southwestern common stock issued in respect of outstanding common stock and stock-based awards (in shares)		337,827,171
Value of Southwestern's stock issued as consideration		$ 1,588,000,000
NYSE closing price per share of Southwestern common shares (in dollars per share)		$ 4.70
Revolving credit facility		$ 95,000,000
Evaluated natural gas and oil properties		2,724,000,000
Unevaluated natural gas and oil properties		684,000,000
Other property, plant and equipment		4,000,000
Operating revenues acquired through the merger						682,000,000
Operating income acquired through the merger						472,000,000
Senior unsecured notes		$ 726,000,000
Montage Resources Corporation
Business Acquisition [Line Items]
Shares of Southwestern common stock issued in respect of outstanding common stock and stock-based awards (in shares)			69,740,848
Value of Southwestern's stock issued as consideration			$ 213,000,000
NYSE closing price per share of Southwestern common shares (in dollars per share)			$ 3.05	$ 2.50
Revolving credit facility			$ 200,000,000
Evaluated natural gas and oil properties			1,012,000,000
Unevaluated natural gas and oil properties			100,000,000
Other property, plant and equipment			28,000,000
Operating revenues acquired through the merger					63,000,000
Operating income acquired through the merger					$ 28,000,000
Senior unsecured notes			$ 522,000,000
Number of Southwestern Energy common stock for each share of common stock converted (in shares)			1.8656
Proved property acquired			$ 1,012,000,000
Unproved property acquired			$ 100,000,000
Montage Resources Corporation | Public Stock Offering
Business Acquisition [Line Items]
Underwritten public offering of common stock (in shares)				63,250,000
Net proceeds from public offering				$ 152,000,000
GEPH Merger
Business Acquisition [Line Items]
Cash consideration	$ 1,269,000,000
Shares of Southwestern common stock issued in respect of outstanding common stock and stock-based awards (in shares)	99,337,748
Value of Southwestern's stock issued as consideration	$ 463,000,000					$ 463,000,000	$ 463,000,000
NYSE closing price per share of Southwestern common shares (in dollars per share)	$ 4.66					$ 4.66	$ 4.66
Revolving credit facility	$ 81,000,000					$ 81,000,000	$ 81,000,000
Evaluated natural gas and oil properties	1,783,000,000					1,783,000,000	1,783,000,000
Unevaluated natural gas and oil properties	59,000,000					59,000,000	59,000,000
Other property, plant and equipment	2,000,000					$ 2,000,000	$ 2,000,000
Operating revenues acquired through the merger	0
Operating income acquired through the merger	$ 0
Senior Notes | 5.375% Senior Notes due February 2029
Business Acquisition [Line Items]
Stated interest rate	5.375%	5.375%				5.375%	5.375%
Long-term debt		$ 700,000,000								$ 700,000,000
Senior Notes | 8.375% Senior Notes due September 2028
Business Acquisition [Line Items]
Stated interest rate	8.375%				8.375%	8.375%	8.375%	8.375%
Long-term debt					$ 345,000,000			$ 345,000,000
Senior notes				$ 350,000,000
Senior Notes | Montage Resources Corporation | Eight Point Eight Seven Five Percent Senior Notes Due 2023
Business Acquisition [Line Items]
Stated interest rate				8.875%
Senior notes				$ 510,000,000
Senior Notes | Indigo Natural Resources, LLC | 5.375% Senior Notes due February 2029
Business Acquisition [Line Items]
Senior note assumed in merger agreement		$ 700,000,000
Stated interest rate		5.375%
Senior Notes | Montage Resources Corporation | 8.375% Senior Notes due September 2028
Business Acquisition [Line Items]
Stated interest rate				8.375%
Senior notes				$ 350,000,000