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Contracts Revenue, Early Termination Of Contract

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Number of fleet of self-elevating mobile offshore jack-up drilling units.

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Number of Drillships.

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Present value of minimum lease payments for operating leases net of executory costs, including amounts paid by the lessee to the lessor for insurance, maintenance and taxes.

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Shares Received After Merger

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Face amount or stated value per share of common stock.

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Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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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 delivery price committed to in the contract.

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Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year.

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Other cash or noncash adjustments to reconcile net income to cash provided by (used in) operating activities that are not separately disclosed in the statement of cash flows (for example, cash received or cash paid during the current period for miscellaneous operating activities, net change during the reporting period in other assets or other liabilities).

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Amount of distribution received from equity method investee for return of investment, classified as investing activities. Excludes distribution for return on investment, classified as operating activities.

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Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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Nature of Operations and Basis of Presentation (Details) $ / shares in Units, $ in Millions			3 Months Ended					9 Months Ended		10 Months Ended	12 Months Ended	15 Months Ended	18 Months Ended
	Oct. 07, 2018 $ / shares	Oct. 01, 2018 USD ($) drilling_unit	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($) $ / d	Mar. 31, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) drilling_unit segment	Sep. 30, 2017 USD ($)	Oct. 16, 2017 segment	Dec. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2017 USD ($)
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Number of Operating Segments \| segment								3		2
Number of ultra-deepwater drillships \| drilling_unit								4
Number of fleet of self-elevating mobile offshore jack-up drilling units \| drilling_unit								23
Due from Joint Venture, Total				$ 269.0				$ 269.0						$ 271.3
Cumulative effect of new accounting principle in period of adoption				5.5			$ 206.6	5.5	$ 206.6
Demobilization related cash payment								10.7	1.8
REVENUE				192.9			291.6	645.4	986.1
Retained earnings [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative effect of new accounting principle in period of adoption				51.1			$ 206.6	51.1	$ 206.6
Accounting Standards Update 2014-09 [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Demobilization related cash payment						$ 5.5
Accounting Standards Update 2014-09 [Member] \| Retained earnings [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative effect of new accounting principle in period of adoption				5.5				5.5
Accounting Standards Update 2016-02 [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Undiscounted future minimum lease commitments				30.0				30.0
Estimated present value of future lease commitments				$ 25.0				$ 25.0
Saudi Arabia Joint Venture [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Number of fleet of self-elevating mobile offshore jack-up drilling units \| drilling_unit								5
Saudi Arabia Joint Venture [Member] \| Saudi Aramco [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Equity Method Investment, Ownership Percentage				50.00%				50.00%
Demobilization [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
REVENUE				$ 5.3				$ 5.3
Parent Company [Member] \| Saudi Arabia Joint Venture [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Equity Method Investment, Ownership Percentage				50.00%				50.00%
Accounting Standards Update 2018-02 [Member] \| Retained earnings [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Cumulative effect of new accounting principle in period of adoption				$ 45.6				$ 45.6
Anadarko [Member] \| Rowan Resolute [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Contracts Revenue, Early Termination Of Contract					$ 27.8
Oil and Gas Delivery Commitments and Contracts, Fixed Price \| $ / d					418,400
Subsequent Event [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Due from Joint Venture, Total		$ 445.0
Subsequent Event [Member] \| Saudi Arabia Joint Venture [Member] \| Saudi Aramco [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Proceeds from Equity Method Investment, Distribution, Return of Capital		$ 90.0
Subsequent Event [Member] \| Parent Company [Member] \| Saudi Arabia Joint Venture [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Additional Number Of Rigs Contributed To Joint Venture \| drilling_unit		2
Proceeds from Equity Method Investment, Distribution, Return of Capital		$ 90.0
Subsequent Event [Member] \| Ensco [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Shares Received by Rowan Shareholders for Rowan Ensco merge \| $ / shares	$ 2.215
Common Stock, Par or Stated Value Per Share \| $ / shares	$ 0.10
Scenario, Forecast [Member] \| Demobilization [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
REVENUE			$ 1.5								$ 1.7	$ 3.2	$ 8.5