Debt - Narrative (Details)	Feb. 01, 2019 USD ($)	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Long-Term Debt Instrument [Line Items]
Debt instrument, face amount						$ 9,978,000,000	$ 8,168,000,000
Senior notes | 6.875% senior notes due 2025
Long-Term Debt Instrument [Line Items]
Debt instrument, face amount	$ 700,000,000					$ 700,000,000	0
Interest rate, stated percentage	6.875%					6.875%
Debt covenant, basket	$ 25,000,000
Revolving credit facility | Chesapeake revolving credit facility
Long-Term Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity						$ 3,000,000,000
Line of credit facility, maximum borrowing capacity, increased maximum						4,000,000,000
Letters of credit outstanding, amount						$ 61,000,000
Leverage ratio	4.00
Fixed charge coverage ratio						2.00
Revolving credit facility | BVL revolving credit facility
Long-Term Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity						$ 2,000,000,000
Line of credit facility, current borrowing capacity						1,300,000,000
Letters of credit outstanding, amount						$ 47,000,000
Mortgage guarantee, secured percent on proved reserves						85.00%
Ratio of net debt to EBITDAX	4.00
Ratio of funded debt o EBITDAX	4.00
Current Ratio	1.00
Revolving credit facility | Line of credit | Chesapeake revolving credit facility
Long-Term Debt Instrument [Line Items]
Debt instrument, face amount						$ 842,000,000	419,000,000
Borrowing capacity available						2,097,000,000
Revolving credit facility | Line of credit | BVL revolving credit facility
Long-Term Debt Instrument [Line Items]
Debt instrument, face amount						$ 688,000,000	$ 0
Minimum | Revolving credit facility | BVL revolving credit facility
Long-Term Debt Instrument [Line Items]
Commitment fee	0.375%
Minimum | Alternative Base Rate (ABR) | Revolving credit facility | Chesapeake revolving credit facility
Long-Term Debt Instrument [Line Items]
Variable rate percentage	0.50%
Minimum | Alternative Base Rate (ABR) | Revolving credit facility | BVL revolving credit facility
Long-Term Debt Instrument [Line Items]
Variable rate percentage	0.50%
Minimum | Eurodollar | Revolving credit facility | BVL revolving credit facility
Long-Term Debt Instrument [Line Items]
Variable rate percentage	1.50%
Minimum | London Interbank Offered Rate (LIBOR) | Revolving credit facility | Chesapeake revolving credit facility
Long-Term Debt Instrument [Line Items]
Variable rate percentage	1.50%
Minimum | London Interbank Offered Rate (LIBOR) | Revolving credit facility | BVL revolving credit facility
Long-Term Debt Instrument [Line Items]
Variable rate percentage	1.50%
Maximum | Revolving credit facility | BVL revolving credit facility
Long-Term Debt Instrument [Line Items]
Commitment fee	0.50%
Maximum | Alternative Base Rate (ABR) | Revolving credit facility | Chesapeake revolving credit facility
Long-Term Debt Instrument [Line Items]
Variable rate percentage	2.00%
Maximum | Alternative Base Rate (ABR) | Revolving credit facility | BVL revolving credit facility
Long-Term Debt Instrument [Line Items]
Variable rate percentage	1.50%
Maximum | Eurodollar | Revolving credit facility | BVL revolving credit facility
Long-Term Debt Instrument [Line Items]
Variable rate percentage	2.50%
Maximum | London Interbank Offered Rate (LIBOR) | Revolving credit facility | Chesapeake revolving credit facility
Long-Term Debt Instrument [Line Items]
Variable rate percentage	3.00%
Maximum | London Interbank Offered Rate (LIBOR) | Revolving credit facility | BVL revolving credit facility
Long-Term Debt Instrument [Line Items]
Variable rate percentage	2.50%
Forecast | Revolving credit facility | Chesapeake revolving credit facility
Long-Term Debt Instrument [Line Items]
Leverage ratio		4.00			5.50
Secured leverage ratio		2.50
Fixed charge coverage ratio			2.50	2.25