LEASES - Supplement balance sheet information (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 drilling_rig	Sep. 30, 2020 USD ($) drilling_rig	Dec. 31, 2019 USD ($)
Leases [Abstract]
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]		us-gaap:OtherAssetsNoncurrent	us-gaap:OtherAssetsNoncurrent
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]		us-gaap:PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization	us-gaap:PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]		us-gaap:AccruedLiabilitiesCurrent	us-gaap:AccruedLiabilitiesCurrent
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]		us-gaap:AccruedLiabilitiesCurrent	us-gaap:AccruedLiabilitiesCurrent
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]		us-gaap:OtherLiabilitiesNoncurrent	us-gaap:OtherLiabilitiesNoncurrent
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]		us-gaap:OtherLiabilitiesNoncurrent	us-gaap:OtherLiabilitiesNoncurrent
Operating lease, net		$ 43	$ 59
Finance lease, net		1	2
Total right-of-use assets		44	61
Operating lease		10	27
Finance lease		1	1
Operating lease		31	37
Finance lease		0	1
Total lease liabilities		$ 42	$ 66
Number of drilling rigs released | drilling_rig	5
Number of drilling rigs remaining | drilling_rig		2