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Acquisition - (Schedule of Consideration Paid to Equity Holders of Indigo (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended	9 Months Ended
	Sep. 01, 2021	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Cash consideration			$ 373	$ 0
Indigo Natural Resources, LLC
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Shares of Southwestern common stock issued	337,827,171	337,827,171
NYSE closing price per share of Southwestern common shares on September 1, 2021 (in dollars per share)	$ 4.70
Business acquisition, equity interest issued	$ 1,588
Cash consideration	373
Total consideration	$ 1,961