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Number of fleet of self-elevating mobile offshore jack-up drilling units purchased [Line Items]

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Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Costs of generating revenue from oil and gas-related services including well services (such as drilling, rigs and analytic evaluations), transportation, and other supporting contractor services, during the reporting period.

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Gain (loss) from sale or disposal of an organization or integrated set of activities (for example, but not limited to, a partnership or corporation) engaged in providing a product or service in a commercial, industrial, or professional environment.

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This item represents the entity's proportionate share for the period of the net income (loss) of its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. This item includes income or expense related to stock-based compensation based on the investor's grant of stock to employees of an equity method investee.

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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The net result for the period of deducting operating expenses from operating revenues.

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The cash outflow for purchases of and capital improvements on property, plant and equipment (capital expenditures), software, and other intangible assets.

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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SEGMENT AND GEOGRAPHIC AREA INFORMATION - Segment (Details) $ in Millions		1 Months Ended	10 Months Ended	12 Months Ended
	Oct. 17, 2017 drilling_unit	Jan. 31, 2018 drilling_unit	Oct. 16, 2017 segment	Dec. 31, 2017 USD ($) segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Segment Reporting [Abstract]
Number of operating segments \| segment			2	3
Segment Reporting Information [Line Items]
Revenues				$ 1,282.8	$ 1,843.2	$ 2,137.0
Direct operating costs (excluding items below)				684.8	778.2	993.1
Depreciation and amortization				403.7	402.9	391.4
Selling, general and administrative				104.9	102.1	115.8
Gain on sale of assets to unconsolidated subsidiary				(157.4)	0.0	0.0
Other operating items				9.4	41.6	329.6
Income (Loss) from Equity Method Investments				0.9	0.0	0.0
INCOME (LOSS) FROM OPERATIONS				238.3	518.4	307.1
Capital expenditures				100.6	117.6	722.9
Total assets (at end of year)				8,458.3	8,675.6
Deposit made for acquisition of rigs				7.7
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues				1,331.4	1,843.2	2,137.0
Direct operating costs (excluding items below)				707.0	778.2	993.1
Depreciation and amortization				416.6	402.9	391.4
Selling, general and administrative				111.0	102.1	115.8
Gain on sale of assets to unconsolidated subsidiary				(157.4)
Other operating items				9.3	41.6	329.6
Income (Loss) from Equity Method Investments				0.0
INCOME (LOSS) FROM OPERATIONS				244.9	518.4	307.1
Operating Segments [Member] \| Deepwater [Member]
Segment Reporting Information [Line Items]
Revenues				467.9	827.5	747.8
Direct operating costs (excluding items below)				151.4	222.0	276.6
Depreciation and amortization				111.6	115.0	94.6
Selling, general and administrative				0.0	0.0	0.0
Gain on sale of assets to unconsolidated subsidiary				0.0
Other operating items				0.1	0.1	0.0
Income (Loss) from Equity Method Investments				0.0
INCOME (LOSS) FROM OPERATIONS				204.8	490.4	376.6
Capital expenditures				8.3	31.5	555.1
Total assets (at end of year)				2,857.6	3,037.7
Operating Segments [Member] \| Jack-ups [Member]
Segment Reporting Information [Line Items]
Revenues				807.5	1,015.7	1,389.2
Direct operating costs (excluding items below)				533.4	556.2	716.5
Depreciation and amortization				289.4	282.6	283.9
Selling, general and administrative				0.0	0.0	0.0
Gain on sale of assets to unconsolidated subsidiary				(157.4)
Other operating items				9.3	40.9	328.8
Income (Loss) from Equity Method Investments				0.0
INCOME (LOSS) FROM OPERATIONS				132.8	136.0	60.0
Capital expenditures				86.4	84.3	128.8
Total assets (at end of year)				4,173.7	4,285.8
Operating Segments [Member] \| ARO Segment [Member]
Segment Reporting Information [Line Items]
Revenues				48.6	0.0	0.0
Direct operating costs (excluding items below)				22.2	0.0	0.0
Depreciation and amortization				12.9	0.0	0.0
Selling, general and administrative				6.1	0.0	0.0
Gain on sale of assets to unconsolidated subsidiary				0.0
Other operating items				(0.1)	0.0	0.0
Income (Loss) from Equity Method Investments				0.0
INCOME (LOSS) FROM OPERATIONS				7.5	0.0	0.0
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Revenues				7.4	0.0	0.0
Direct operating costs (excluding items below)				0.0	0.0	0.0
Depreciation and amortization				2.7	5.3	12.9
Selling, general and administrative				104.9	102.1	115.8
Gain on sale of assets to unconsolidated subsidiary				0.0
Other operating items				0.0	0.6	0.8
Income (Loss) from Equity Method Investments				0.0
INCOME (LOSS) FROM OPERATIONS				(100.2)	(108.0)	(129.5)
Capital expenditures				5.9	1.8	39.0
Total assets (at end of year)				1,427.0	1,352.1
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues				(48.6)	0.0	0.0
Direct operating costs (excluding items below)				(22.2)	0.0	0.0
Depreciation and amortization				(12.9)	0.0	0.0
Selling, general and administrative				(6.1)	0.0	0.0
Gain on sale of assets to unconsolidated subsidiary				0.0
Other operating items				0.1	0.0	0.0
Income (Loss) from Equity Method Investments				0.9
INCOME (LOSS) FROM OPERATIONS				$ (6.6)	$ 0.0	$ 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	3
Subsequent Event [Member]
Segment Reporting Information [Line Items]
Number of fleet of self-elevating mobile offshore jack-up drilling units purchased \| drilling_unit		2