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SEGMENT AND GEOGRAPHIC AREA INFORMATION - Segment (Details) $ in Millions			10 Months Ended	12 Months Ended
	Oct. 01, 2018 drilling_unit	Oct. 17, 2017 drilling_unit	Oct. 16, 2017 segment	Dec. 31, 2018 USD ($) segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments \| segment			2	3
REVENUE				$ 824.8	$ 1,282.8	$ 1,843.2
Direct operating costs (excluding items below)				682.7	685.0	779.7
Depreciation and amortization				388.9	403.7	402.9
Selling, general and administrative				96.1	104.6	102.2
Gain on sale of assets to unconsolidated subsidiary				(65.8)	(157.4)	0.0
Other operating items				12.1	9.4	41.6
Merger and related costs				8.9	0.0	0.0
Equity in earnings of unconsolidated subsidiary				10.3	0.9	0.0
INCOME (LOSS) FROM OPERATIONS				(287.8)	238.4	516.8
Capital expenditures				169.2	100.6	117.6
Total assets (at end of year)				8,117.7	8,458.3
Deepwater [Member]
Segment Reporting Information [Line Items]
REVENUE				158.1	467.9	827.5
Jack-ups [Member]
Segment Reporting Information [Line Items]
REVENUE				632.9	807.5	1,015.7
Operating Segments [Member]
Segment Reporting Information [Line Items]
REVENUE				1,173.6	1,331.4	1,843.2
Direct operating costs (excluding items below)				876.7	707.2	779.7
Depreciation and amortization				456.3	416.6	402.9
Selling, general and administrative				123.1	110.7	102.2
Gain on sale of assets to unconsolidated subsidiary				(65.8)	(157.4)
Other operating items				13.5	9.3	41.6
Merger and related costs				8.9
Equity in earnings of unconsolidated subsidiary				0.0	0.0
INCOME (LOSS) FROM OPERATIONS				(239.1)	245.0	516.8
Operating Segments [Member] \| Deepwater [Member]
Segment Reporting Information [Line Items]
REVENUE				158.1	467.9	827.5
Direct operating costs (excluding items below)				168.6	151.4	222.4
Depreciation and amortization				108.5	111.6	115.0
Selling, general and administrative				0.0	0.0	0.0
Gain on sale of assets to unconsolidated subsidiary				0.0	0.0
Other operating items				1.6	0.1	0.1
Merger and related costs				0.0
Equity in earnings of unconsolidated subsidiary				0.0	0.0
INCOME (LOSS) FROM OPERATIONS				(120.6)	204.8	490.0
Capital expenditures				16.7	8.3	31.5
Total assets (at end of year)				2,757.9	2,857.6
Operating Segments [Member] \| Jack-ups [Member]
Segment Reporting Information [Line Items]
REVENUE				632.9	807.5	1,015.7
Direct operating costs (excluding items below)				514.1	533.6	557.3
Depreciation and amortization				278.3	289.4	282.6
Selling, general and administrative				0.0	0.0	0.0
Gain on sale of assets to unconsolidated subsidiary				(65.8)	(157.4)
Other operating items				5.3	9.3	40.9
Merger and related costs				0.0
Equity in earnings of unconsolidated subsidiary				0.0	0.0
INCOME (LOSS) FROM OPERATIONS				(99.0)	132.6	134.9
Capital expenditures				145.8	86.4	84.3
Total assets (at end of year)				4,153.8	4,173.7
Operating Segments [Member] \| ARO Segment [Member]
Segment Reporting Information [Line Items]
REVENUE				348.8	48.6	0.0
Direct operating costs (excluding items below)				194.0	22.2	0.0
Depreciation and amortization				67.4	12.9	0.0
Selling, general and administrative				27.0	6.1	0.0
Gain on sale of assets to unconsolidated subsidiary				0.0	0.0
Other operating items				1.4	(0.1)	0.0
Merger and related costs				0.0
Equity in earnings of unconsolidated subsidiary				0.0	0.0
INCOME (LOSS) FROM OPERATIONS				59.0	7.5	0.0
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
REVENUE				33.8	7.4	0.0
Direct operating costs (excluding items below)				0.0	0.0	0.0
Depreciation and amortization				2.1	2.7	5.3
Selling, general and administrative				96.1	104.6	102.2
Gain on sale of assets to unconsolidated subsidiary				0.0	0.0
Other operating items				5.2	0.0	0.6
Merger and related costs				8.9
Equity in earnings of unconsolidated subsidiary				0.0	0.0
INCOME (LOSS) FROM OPERATIONS				(78.5)	(99.9)	(108.1)
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Capital expenditures				6.7	5.9	1.8
Total assets (at end of year)				1,206.0	1,427.0
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
REVENUE				(348.8)	(48.6)	0.0
Direct operating costs (excluding items below)				(194.0)	(22.2)	0.0
Depreciation and amortization				(67.4)	(12.9)	0.0
Selling, general and administrative				(27.0)	(6.1)	0.0
Gain on sale of assets to unconsolidated subsidiary				0.0	0.0
Other operating items				(1.4)	0.1	0.0
Merger and related costs				0.0
Equity in earnings of unconsolidated subsidiary				10.3	0.9
INCOME (LOSS) FROM OPERATIONS				(48.7)	(6.6)	$ 0.0
Rowan Companies plc (Parent) [Member] \| Saudi Arabia Joint Venture [Member]
Segment Reporting Information [Line Items]
Initial Number Of Rigs Contributed To Joint Venture \| drilling_unit	2	3
Equity in earnings of unconsolidated subsidiary				$ 10.3	$ 0.9
Equity Method Investment, Ownership Percentage				50.00%
Saudi Aramco [Member] \| Saudi Arabia Joint Venture [Member]
Segment Reporting Information [Line Items]
Initial Number Of Rigs Contributed To Joint Venture \| drilling_unit		1
Equity Method Investment, Ownership Percentage				50.00%