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NATURE OF OPERATIONS AND BASIS OF PRESENTATION (Details) $ / shares in Units, $ in Millions			2 Months Ended	3 Months Ended				6 Months Ended	10 Months Ended	12 Months Ended
	Jan. 28, 2019 $ / shares	May 23, 2016 USD ($)	May 22, 2016 USD ($)	Jun. 30, 2018 USD ($) $ / d	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017	Oct. 16, 2017 segment	Dec. 31, 2018 USD ($) drilling_unit segment	Dec. 31, 2017 USD ($) $ / d	Dec. 31, 2016 $ / bbl	Sep. 15, 2016 USD ($) $ / d
Disaggregation of Revenue [Line Items]
Number of operating segments \| segment									2	3
Number of Drillships \| drilling_unit										4
Number of fleet of self-elevating mobile offshore jack-up drilling units \| drilling_unit										21
Deferred revenue										$ 16.7	$ 1.1
Less: amortization										$ 16.8
Rowan Relentless [Member]
Disaggregation of Revenue [Line Items]
Revenue, canceled contract value							$ 130.9
Contingent payments, period of evaluation		12 months						12 months
Revenue			$ 30.5				173.2
Revenue, fair value of derivative associated with early contract termination agreement							6.2
Less: amortization							$ 5.6
Outstanding Receivables From Early Contract Termination [Member] \| Rowan Relentless [Member]
Disaggregation of Revenue [Line Items]
Outstanding receivables from early termination of contract		$ 215.0
Contingent Consideration Threshold 1 [Member] \| Rowan Relentless [Member]
Disaggregation of Revenue [Line Items]
Additional contingent payments		10.0
Contingent payment, threshold price per barrel (in USD per bbl) \| $ / bbl												50
Contingent Consideration Threshold 2 [Member] \| Rowan Relentless [Member]
Disaggregation of Revenue [Line Items]
Additional contingent payments		$ 20.0
Contingent payment, threshold price per barrel (in USD per bbl) \| $ / bbl												65
Saudi Arabia Joint Venture [Member]
Disaggregation of Revenue [Line Items]
Number of fleet of self-elevating mobile offshore jack-up drilling units \| drilling_unit										7
Period Of Joint Venture Funding Of Drilling Rigs										10 years
Anadarko [Member] \| Rowan Resolute [Member]
Disaggregation of Revenue [Line Items]
Revenue, canceled contract value				$ 27.8
Day rate (in USD per day) \| $ / d				418,400
Cobalt International [Member]
Disaggregation of Revenue [Line Items]
Exclusive provider contract term (in years)											5 years
Cobalt International [Member] \| Rowan Reliance [Member]
Disaggregation of Revenue [Line Items]
Day rate (in USD per day) \| $ / d													582,000
Outstanding receivables from early termination of contract													$ 95.9
Day rate, after March 31, 2017 (in USD per day) \| $ / d											262,000
Cobalt International [Member] \| Outstanding Receivables From Early Contract Termination [Member] \| Rowan Reliance [Member]
Disaggregation of Revenue [Line Items]
Outstanding receivables from early termination contract, cash received in period					$ 19.6	$ 76.3
Deferred Revenue [Domain] \| Cobalt International [Member] \| Rowan Reliance [Member]
Disaggregation of Revenue [Line Items]
Deferred revenue													$ 95.9
Rowan Companies plc (Parent) [Member] \| Saudi Arabia Joint Venture [Member]
Disaggregation of Revenue [Line Items]
Equity Method Investment, Ownership Percentage										50.00%
Saudi Aramco [Member] \| Saudi Arabia Joint Venture [Member]
Disaggregation of Revenue [Line Items]
Equity Method Investment, Ownership Percentage										50.00%
Ensco [Member]
Disaggregation of Revenue [Line Items]
Business Combination, Termination fee due to other merge transaction										$ 24.0
Rowan [Member]
Disaggregation of Revenue [Line Items]
Business Combination, Termination fee due to other merge transaction										$ 24.0
Subsequent Event [Member] \| Ensco [Member]
Disaggregation of Revenue [Line Items]
Shares Received after Merger \| $ / shares	$ 2.750
Common Stock, Par or Stated Value Per Share \| $ / shares	$ 0.10
Maximum [Member] \| Saudi Arabia Joint Venture [Member]
Disaggregation of Revenue [Line Items]
Number Of Drilling Rigs To Be Purchased By Joint Venture \| drilling_unit										20