Guarantees of Registered Securities - Condensed Consolidating Financial Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Dec. 31, 2017
Condensed Consolidating Income Statements
REVENUE	$ 192.9	$ 291.6	$ 645.4	$ 986.1
COSTS AND EXPENSES:
Direct operating costs (excluding items below)	182.3	168.7	516.0	508.8
Depreciation and amortization	99.0	103.4	294.3	304.0
Selling, general and administrative	26.6	24.9	77.4	71.3
Loss on disposals of property and equipment	1.5	2.8	5.0	9.3
Total costs and expenses	309.4	299.8	892.7	893.4
Equity in earnings of unconsolidated subsidiary	3.1	0.0	3.4	0.0
INCOME (LOSS) FROM OPERATIONS	(113.4)	(8.2)	(243.9)	92.7
OTHER INCOME (EXPENSE):
Interest expense	(39.2)	(38.5)	(116.6)	(117.0)
Interest income	8.0	3.7	22.6	8.9
Gain (loss) on extinguishment of debt	0.0	(0.5)	0.0	1.7
Other - net	4.0	0.8	10.6	3.7
Total other (expense) - net	(27.2)	(34.5)	(83.4)	(102.7)
LOSS BEFORE INCOME TAXES	(140.6)	(42.7)	(327.3)	(10.0)
Provision (benefit) for income taxes	3.5	(21.8)	5.8	29.3
Equity in earnings (losses) of subsidiaries, net of tax	0.0	0.0	0.0	0.0
NET LOSS	(144.1)	(20.9)	(333.1)	(39.3)
Statements of Comprehensive Income (Loss)
NET INCOME (LOSS)	(144.1)	(20.9)	(333.1)	(39.3)
OTHER COMPREHENSIVE LOSS:
Net changes in pension and other postretirement plan assets and benefit obligations recognized in other comprehensive income, net of income tax expense of $0 for both the three months ended September 30, 2018 and 2017, and $4.2 and $0 for the nine months ended September 30, 2018 and 2017, respectively (see Note 5).	0.0	0.0	15.9	0.0
Net reclassification adjustment for amounts recognized in net loss as a component of net periodic benefit cost, net of income taxes	(0.7)	1.0	4.0	2.7
Total Other Comprehensive Income	(0.7)	1.0	19.9	2.7
COMPREHENSIVE LOSS	(144.8)	(19.9)	(313.2)	(36.6)
CURRENT ASSETS:
Cash and cash equivalents	1,032.4	1,220.0	1,332.1	1,255.5	$ 1,032.4	$ 1,332.1
Receivables - trade and other					281.5	212.8
Prepaid expenses and other current assets					31.4	15.5
Total current assets					1,345.3	1,560.4
Property and equipment - gross					9,005.0	8,833.9
Less accumulated depreciation and amortization					2,566.9	2,281.2
Property and equipment - net					6,438.1	6,552.7
Investment in Consolidated Subsidiary					0.0	0.0
Due from affiliates					0.0	0.0
Long-term note receivable from unconsolidated subsidiary					269.0	270.2
Investment in unconsolidated subsidiary					34.3	30.9
Other assets					44.7	44.1
TOTAL ASSETS					8,131.4	8,458.3
CURRENT LIABILITIES:
Current portion of long-term debt					201.1	0.0
Accounts payable - trade					112.2	97.2
Deferred revenues					17.8	1.1
Accrued liabilities					122.2	159.1
Total current liabilities					453.3	257.4
Long-term debt					2,309.6	2,510.3
Due to affiliates					0.0	0.0
Other liabilities					268.6	293.6
Deferred income taxes - net					11.1	10.9
Shareholders' equity					5,088.8	5,386.1
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY					8,131.4	8,458.3
Consolidating Statements of Cash Flows
Net cash provided by (used in) operating activities			(112.4)	241.0
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures			(116.9)	(78.6)
Purchase of rigs			(70.8)
Proceeds from disposals of property and equipment			8.1	1.5
Contributions to consolidated subsidiary for note receivable			0.0
Investments in consolidated subsidiaries			0.0	0.0
Investment in unconsolidated subsidiary			0.0	(25.0)
Repayments of note receivable from unconsolidated subsidiary			2.3	0.0
Net cash used in investing activities			(177.3)	(102.1)
CASH FLOWS FROM FINANCING ACTIVITIES:
Advances (to) from affiliates			0.0	0.0
Distribution to issuer			0.0	0.0
Proceeds From Borrowings Net Of Issue Costs			0.0
Reductions of long-term debt			0.0	(170.0)
Debt issue costs			(6.1)	0.0
Proceeds from exercise of share options			(3.9)	(4.4)
Dividends paid				0.0
Net cash used in financing activities			(10.0)	(174.4)
DECREASE IN CASH AND CASH EQUIVALENTS			(299.7)	(35.5)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD			1,332.1	1,255.5
CASH AND CASH EQUIVALENTS, END OF PERIOD	1,032.4	1,220.0	1,032.4	1,220.0
Consolidating adjustments [Member]
Condensed Consolidating Income Statements
REVENUE	(1.7)	(0.8)	(3.7)	(38.7)
COSTS AND EXPENSES:
Direct operating costs (excluding items below)	0.0	(3.2)	0.0	(34.6)
Depreciation and amortization	0.0	0.0	0.0	0.2
Selling, general and administrative	(1.7)	2.4	(3.7)	(4.3)
Loss on disposals of property and equipment	0.0	0.0	0.0	0.0
Total costs and expenses	(1.7)	(0.8)	(3.7)	(38.7)
Equity in earnings of unconsolidated subsidiary	0.0		0.0
INCOME (LOSS) FROM OPERATIONS	0.0	0.0	0.0	0.0
OTHER INCOME (EXPENSE):
Interest expense	0.5	0.1	1.4	0.4
Interest income	(0.5)	(0.1)	(1.4)	(0.4)
Gain (loss) on extinguishment of debt		0.0		0.0
Other - net	0.0	0.0	0.0	0.0
Total other (expense) - net	0.0	0.0	0.0	0.0
LOSS BEFORE INCOME TAXES	0.0	0.0	0.0	0.0
Provision (benefit) for income taxes	0.0	1.0	0.0
Equity in earnings (losses) of subsidiaries, net of tax	102.3	(28.6)	189.4	(30.8)
NET LOSS	102.3	(29.6)	189.4	(30.8)
Statements of Comprehensive Income (Loss)
NET INCOME (LOSS)	102.3	(29.6)	189.4	(30.8)
OTHER COMPREHENSIVE LOSS:
Net changes in pension and other postretirement plan assets and benefit obligations recognized in other comprehensive income, net of income tax expense of $0 for both the three months ended September 30, 2018 and 2017, and $4.2 and $0 for the nine months ended September 30, 2018 and 2017, respectively (see Note 5).			(15.9)
Net reclassification adjustment for amounts recognized in net loss as a component of net periodic benefit cost, net of income taxes	0.7	(1.0)	(4.0)	(2.7)
Total Other Comprehensive Income			(19.9)
COMPREHENSIVE LOSS	103.0	(30.6)	169.5	(33.5)
CURRENT ASSETS:
Cash and cash equivalents	0.0	0.0	0.0	0.0	0.0	0.0
Receivables - trade and other					0.0	0.0
Prepaid expenses and other current assets					0.0	0.0
Total current assets					0.0	0.0
Property and equipment - gross					0.0	0.0
Less accumulated depreciation and amortization					0.0	0.0
Property and equipment - net					0.0	0.0
Investment in Consolidated Subsidiary					(11,651.7)	(11,788.2)
Due from affiliates					(782.3)	(691.7)
Long-term note receivable from unconsolidated subsidiary					0.0	0.0
Investment in unconsolidated subsidiary					0.0	0.0
Other assets					0.0	0.0
TOTAL ASSETS					(12,434.0)	(12,479.9)
CURRENT LIABILITIES:
Current portion of long-term debt					0.0
Accounts payable - trade					0.0	0.0
Deferred revenues					0.0	0.0
Accrued liabilities					0.0	0.0
Total current liabilities					0.0	0.0
Long-term debt					0.0	0.0
Due to affiliates					(782.3)	(691.7)
Other liabilities					0.0	0.0
Deferred income taxes - net					0.0	0.0
Shareholders' equity					(11,651.7)	(11,788.2)
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY					(12,434.0)	(12,479.9)
Consolidating Statements of Cash Flows
Net cash provided by (used in) operating activities			0.0	(15.0)
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures			0.0	0.0
Purchase of rigs			0.0
Proceeds from disposals of property and equipment			0.0	0.0
Contributions to consolidated subsidiary for note receivable			1.9
Investments in consolidated subsidiaries			5.0	(70.7)
Investment in unconsolidated subsidiary				0.0
Repayments of note receivable from unconsolidated subsidiary			0.0
Net cash used in investing activities			6.9	(70.7)
CASH FLOWS FROM FINANCING ACTIVITIES:
Advances (to) from affiliates			0.0	0.0
Distribution to issuer			(5.0)	70.7
Proceeds From Borrowings Net Of Issue Costs			(1.9)
Reductions of long-term debt				0.0
Debt issue costs			0.0
Proceeds from exercise of share options			0.0	0.0
Dividends paid				15.0
Net cash used in financing activities			(6.9)	85.7
DECREASE IN CASH AND CASH EQUIVALENTS			0.0	0.0
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD			0.0	0.0
CASH AND CASH EQUIVALENTS, END OF PERIOD	0.0	0.0	0.0	0.0
Rowan plc (Parent) [Member] | Reportable Legal Entities [Member]
Condensed Consolidating Income Statements
REVENUE	0.0	0.0	0.0	0.0
COSTS AND EXPENSES:
Direct operating costs (excluding items below)	0.0	0.0	0.0	0.0
Depreciation and amortization	0.0	0.0	0.0	0.0
Selling, general and administrative	7.6	7.0	20.3	18.8
Loss on disposals of property and equipment	0.0	0.0	0.0	0.0
Total costs and expenses	7.6	7.0	20.3	18.8
Equity in earnings of unconsolidated subsidiary	0.0		0.0
INCOME (LOSS) FROM OPERATIONS	(7.6)	(7.0)	(20.3)	(18.8)
OTHER INCOME (EXPENSE):
Interest expense	0.0	0.0	0.0	0.0
Interest income	0.0	0.0	0.0	0.0
Gain (loss) on extinguishment of debt		0.0		0.0
Other - net	5.1	5.1	15.1	15.4
Total other (expense) - net	5.1	5.1	15.1	15.4
LOSS BEFORE INCOME TAXES	(2.5)	(1.9)	(5.2)	(3.4)
Provision (benefit) for income taxes	0.0	0.0	0.0	0.0
Equity in earnings (losses) of subsidiaries, net of tax	(141.6)	(19.0)	(327.9)	(35.9)
NET LOSS	(144.1)	(20.9)	(333.1)	(39.3)
Statements of Comprehensive Income (Loss)
NET INCOME (LOSS)	(144.1)	(20.9)	(333.1)	(39.3)
OTHER COMPREHENSIVE LOSS:
Net changes in pension and other postretirement plan assets and benefit obligations recognized in other comprehensive income, net of income tax expense of $0 for both the three months ended September 30, 2018 and 2017, and $4.2 and $0 for the nine months ended September 30, 2018 and 2017, respectively (see Note 5).			15.9
Net reclassification adjustment for amounts recognized in net loss as a component of net periodic benefit cost, net of income taxes	(0.7)	1.0	4.0	2.7
Total Other Comprehensive Income			19.9
COMPREHENSIVE LOSS	(144.8)	(19.9)	(313.2)	(36.6)
CURRENT ASSETS:
Cash and cash equivalents	0.1	0.3	0.2	3.7	0.1	0.2
Receivables - trade and other					0.0	0.0
Prepaid expenses and other current assets					0.4	0.3
Total current assets					0.5	0.5
Property and equipment - gross					0.0	0.0
Less accumulated depreciation and amortization					0.0	0.0
Property and equipment - net					0.0	0.0
Investment in Consolidated Subsidiary					5,111.6	5,401.1
Due from affiliates					0.2	0.2
Long-term note receivable from unconsolidated subsidiary					0.0	0.0
Investment in unconsolidated subsidiary					0.0	0.0
Other assets					0.0	0.0
TOTAL ASSETS					5,112.3	5,401.8
CURRENT LIABILITIES:
Current portion of long-term debt					0.0
Accounts payable - trade					0.6	0.7
Deferred revenues					0.0	0.0
Accrued liabilities					0.0	0.0
Total current liabilities					0.6	0.7
Long-term debt					0.0	0.0
Due to affiliates					18.3	11.2
Other liabilities					4.6	3.8
Deferred income taxes - net					0.0	0.0
Shareholders' equity					5,088.8	5,386.1
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY					5,112.3	5,401.8
Consolidating Statements of Cash Flows
Net cash provided by (used in) operating activities			(4.7)	(6.1)
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures			0.0	0.0
Purchase of rigs			0.0
Proceeds from disposals of property and equipment			0.0	0.0
Contributions to consolidated subsidiary for note receivable			0.0
Investments in consolidated subsidiaries			0.0	0.0
Investment in unconsolidated subsidiary				0.0
Repayments of note receivable from unconsolidated subsidiary			0.0
Net cash used in investing activities			0.0	0.0
CASH FLOWS FROM FINANCING ACTIVITIES:
Advances (to) from affiliates			8.5	7.1
Distribution to issuer			0.0	0.0
Proceeds From Borrowings Net Of Issue Costs			0.0
Reductions of long-term debt				0.0
Debt issue costs			0.0
Proceeds from exercise of share options			(3.9)	(4.4)
Dividends paid				0.0
Net cash used in financing activities			4.6	2.7
DECREASE IN CASH AND CASH EQUIVALENTS			(0.1)	(3.4)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD			0.2	3.7
CASH AND CASH EQUIVALENTS, END OF PERIOD	0.1	0.3	0.1	0.3
RCI (Issuer) [Member] | Reportable Legal Entities [Member]
Condensed Consolidating Income Statements
REVENUE	1.7	0.6	3.7	38.2
COSTS AND EXPENSES:
Direct operating costs (excluding items below)	0.0	0.4	0.0	1.2
Depreciation and amortization	0.0	4.4	0.0	14.4
Selling, general and administrative	0.0	0.1	0.5	2.0
Loss on disposals of property and equipment	(0.7)	(0.1)	(0.1)	1.6
Total costs and expenses	(0.7)	4.8	0.4	19.2
Equity in earnings of unconsolidated subsidiary	0.0		0.0
INCOME (LOSS) FROM OPERATIONS	2.4	(4.2)	3.3	19.0
OTHER INCOME (EXPENSE):
Interest expense	(37.3)	(38.5)	(113.8)	(117.1)
Interest income	0.5	0.9	2.5	2.6
Gain (loss) on extinguishment of debt		(0.5)		1.7
Other - net	(4.5)	(5.0)	(12.3)	(14.6)
Total other (expense) - net	(41.3)	(43.1)	(123.6)	(127.4)
LOSS BEFORE INCOME TAXES	(38.9)	(47.3)	(120.3)	(108.4)
Provision (benefit) for income taxes	3.8	(0.6)	(3.7)	(10.8)
Equity in earnings (losses) of subsidiaries, net of tax	39.3	47.6	138.5	66.7
NET LOSS	(3.4)	0.9	21.9	(30.9)
Statements of Comprehensive Income (Loss)
NET INCOME (LOSS)	(3.4)	0.9	21.9	(30.9)
OTHER COMPREHENSIVE LOSS:
Net changes in pension and other postretirement plan assets and benefit obligations recognized in other comprehensive income, net of income tax expense of $0 for both the three months ended September 30, 2018 and 2017, and $4.2 and $0 for the nine months ended September 30, 2018 and 2017, respectively (see Note 5).			15.9
Net reclassification adjustment for amounts recognized in net loss as a component of net periodic benefit cost, net of income taxes	(0.7)	1.0	4.0	2.7
Total Other Comprehensive Income			19.9
COMPREHENSIVE LOSS	(4.1)	1.9	41.8	(28.2)
CURRENT ASSETS:
Cash and cash equivalents	14.9	275.5	206.3	532.0	14.9	206.3
Receivables - trade and other					1.1	1.2
Prepaid expenses and other current assets					13.6	10.7
Total current assets					29.6	218.2
Property and equipment - gross					255.4	241.9
Less accumulated depreciation and amortization					136.5	121.4
Property and equipment - net					118.9	120.5
Investment in Consolidated Subsidiary					6,540.1	6,387.1
Due from affiliates					748.9	680.0
Long-term note receivable from unconsolidated subsidiary					0.0	0.0
Investment in unconsolidated subsidiary					0.0	0.0
Other assets					33.3	36.4
TOTAL ASSETS					7,470.8	7,442.2
CURRENT LIABILITIES:
Current portion of long-term debt					201.1
Accounts payable - trade					15.9	12.9
Deferred revenues					0.0	0.0
Accrued liabilities					78.5	95.7
Total current liabilities					295.5	108.6
Long-term debt					2,309.6	2,510.3
Due to affiliates					31.7	11.4
Other liabilities					222.9	261.2
Deferred income taxes - net					0.0	0.0
Shareholders' equity					4,611.1	4,550.7
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY					7,470.8	7,442.2
Consolidating Statements of Cash Flows
Net cash provided by (used in) operating activities			(139.4)	22.0
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures			(5.6)	(17.9)
Purchase of rigs			0.0
Proceeds from disposals of property and equipment			0.2	0.9
Contributions to consolidated subsidiary for note receivable			(1.9)
Investments in consolidated subsidiaries			(5.0)	70.7
Investment in unconsolidated subsidiary				0.0
Repayments of note receivable from unconsolidated subsidiary			0.0
Net cash used in investing activities			(12.3)	53.7
CASH FLOWS FROM FINANCING ACTIVITIES:
Advances (to) from affiliates			(39.7)	(162.2)
Distribution to issuer			0.0	0.0
Proceeds From Borrowings Net Of Issue Costs			0.0
Reductions of long-term debt				(170.0)
Debt issue costs			0.0
Proceeds from exercise of share options			0.0	0.0
Dividends paid				0.0
Net cash used in financing activities			(39.7)	(332.2)
DECREASE IN CASH AND CASH EQUIVALENTS			(191.4)	(256.5)
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD			206.3	532.0
CASH AND CASH EQUIVALENTS, END OF PERIOD	14.9	275.5	14.9	275.5
Non-guarantor subsidiaries [Member] | Reportable Legal Entities [Member]
Condensed Consolidating Income Statements
REVENUE	192.9	291.8	645.4	986.6
COSTS AND EXPENSES:
Direct operating costs (excluding items below)	182.3	171.5	516.0	542.2
Depreciation and amortization	99.0	99.0	294.3	289.4
Selling, general and administrative	20.7	15.4	60.3	54.8
Loss on disposals of property and equipment	2.2	2.9	5.1	7.7
Total costs and expenses	304.2	288.8	875.7	894.1
Equity in earnings of unconsolidated subsidiary	3.1		3.4
INCOME (LOSS) FROM OPERATIONS	(108.2)	3.0	(226.9)	92.5
OTHER INCOME (EXPENSE):
Interest expense	(2.4)	(0.1)	(4.2)	(0.3)
Interest income	8.0	2.9	21.5	6.7
Gain (loss) on extinguishment of debt		0.0		0.0
Other - net	3.4	0.7	7.8	2.9
Total other (expense) - net	9.0	3.5	25.1	9.3
LOSS BEFORE INCOME TAXES	(99.2)	6.5	(201.8)	101.8
Provision (benefit) for income taxes	(0.3)	(22.2)	9.5	40.1
Equity in earnings (losses) of subsidiaries, net of tax	0.0	0.0	0.0	0.0
NET LOSS	(98.9)	28.7	(211.3)	61.7
Statements of Comprehensive Income (Loss)
NET INCOME (LOSS)	(98.9)	28.7	(211.3)	61.7
OTHER COMPREHENSIVE LOSS:
Net changes in pension and other postretirement plan assets and benefit obligations recognized in other comprehensive income, net of income tax expense of $0 for both the three months ended September 30, 2018 and 2017, and $4.2 and $0 for the nine months ended September 30, 2018 and 2017, respectively (see Note 5).			0.0
Net reclassification adjustment for amounts recognized in net loss as a component of net periodic benefit cost, net of income taxes	0.0	0.0	0.0	0.0
Total Other Comprehensive Income			0.0
COMPREHENSIVE LOSS	(98.9)	28.7	(211.3)	61.7
CURRENT ASSETS:
Cash and cash equivalents	1,017.4	944.2	1,125.6	719.8	1,017.4	1,125.6
Receivables - trade and other					280.4	211.6
Prepaid expenses and other current assets					17.4	4.5
Total current assets					1,315.2	1,341.7
Property and equipment - gross					8,749.6	8,592.0
Less accumulated depreciation and amortization					2,430.4	2,159.8
Property and equipment - net					6,319.2	6,432.2
Investment in Consolidated Subsidiary					0.0	0.0
Due from affiliates					33.2	11.5
Long-term note receivable from unconsolidated subsidiary					269.0	270.2
Investment in unconsolidated subsidiary					34.3	30.9
Other assets					11.4	7.7
TOTAL ASSETS					7,982.3	8,094.2
CURRENT LIABILITIES:
Current portion of long-term debt					0.0
Accounts payable - trade					95.7	83.6
Deferred revenues					17.8	1.1
Accrued liabilities					43.7	63.4
Total current liabilities					157.2	148.1
Long-term debt					0.0	0.0
Due to affiliates					732.3	669.1
Other liabilities					41.1	28.6
Deferred income taxes - net					11.1	10.9
Shareholders' equity					7,040.6	7,237.5
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY					$ 7,982.3	$ 8,094.2
Consolidating Statements of Cash Flows
Net cash provided by (used in) operating activities			31.7	240.1
CASH FLOWS FROM INVESTING ACTIVITIES:
Capital expenditures			(111.3)	(60.7)
Purchase of rigs			(70.8)
Proceeds from disposals of property and equipment			7.9	0.6
Contributions to consolidated subsidiary for note receivable			0.0
Investments in consolidated subsidiaries			0.0	0.0
Investment in unconsolidated subsidiary				(25.0)
Repayments of note receivable from unconsolidated subsidiary			2.3
Net cash used in investing activities			(171.9)	(85.1)
CASH FLOWS FROM FINANCING ACTIVITIES:
Advances (to) from affiliates			31.2	155.1
Distribution to issuer			5.0	(70.7)
Proceeds From Borrowings Net Of Issue Costs			1.9
Reductions of long-term debt				0.0
Debt issue costs			(6.1)
Proceeds from exercise of share options			0.0	0.0
Dividends paid				(15.0)
Net cash used in financing activities			32.0	69.4
DECREASE IN CASH AND CASH EQUIVALENTS			(108.2)	224.4
CASH AND CASH EQUIVALENTS, BEGINNING OF PERIOD			1,125.6	719.8
CASH AND CASH EQUIVALENTS, END OF PERIOD	$ 1,017.4	$ 944.2	$ 1,017.4	$ 944.2