Revolving Credit Facilities (Details)		3 Months Ended
	Mar. 08, 2018 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Aug. 20, 2018 USD ($)	Mar. 07, 2018 USD ($)	Dec. 31, 2017 USD ($)
Short-term Debt [Line Items]
Number of days outstanding, prior to springing maturity date	91 days
Value of proved reserves, percentage to mortgage	80.00%
Value of proved developing producing reserves, percentage to mortgage	80.00%
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Credit facility, face amount	$ 2,100,000,000				$ 1,500,000,000
Accordion feature, increased commitment	3,000,000,000
Initial borrowing base	2,500,000,000			$ 2,100,000,000	2,000,000,000
Letters of credit aggregate sub-limit	$ 650,000,000
Minimum threshold to activate springing maturity date		$ 500,000,000
Maximum net leverage ratio	4.00
Minimum current ratio	1
Borrowings outstanding			$ 439,000,000			$ 0
Letters of credit outstanding			251,342,000			239,072,000
Borrowings and issuance of letters of credit remaining capacity			$ 1,409,658,000			$ 1,260,928,000
5.875% Senior Notes due 2022 [Member]
Short-term Debt [Line Items]
Stated rate, debt instrument			5.875%
CNXM [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Letters of credit aggregate sub-limit	$ 600,000,000				$ 250,000,000
Borrowings outstanding			$ 44,000,000
Secured leverage ratio	3.5
Interest coverage ratio	2.5
CNXM [Member] | Minimum [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Maximum net leverage ratio	4.75
CNXM [Member] | Maximum [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Maximum net leverage ratio	5.50