Income Taxes	3 Months Ended
Mar. 31, 2019
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract]
Income Taxes	Income Taxes Ensco Rowan plc, our parent company, is domiciled and resident in the U.K. Our subsidiaries conduct operations and earn income in numerous countries and are subject to the laws of taxing jurisdictions within those countries. The income of our non-U.K. subsidiaries is generally not subject to U.K. taxation. Income tax rates imposed in the tax jurisdictions in which our subsidiaries conduct operations vary, as does the tax base to which the rates are applied. In some cases, tax rates may be applicable to gross revenues, statutory or negotiated deemed profits or other bases utilized under local tax laws, rather than to net income. Therefore, we generally incur income tax expense in periods in which we operate at a loss. Our drilling rigs frequently move from one taxing jurisdiction to another to perform contract drilling services. In some instances, the movement of our drilling rigs among taxing jurisdictions will involve the transfer of ownership of the drilling rigs among our subsidiaries. As a result of frequent changes in the taxing jurisdictions in which our drilling rigs are operated and/or owned, changes in the overall level of our income and changes in tax laws, our consolidated effective income tax rate may vary substantially from one reporting period to another. Income tax rates and taxation systems in the jurisdictions in which our subsidiaries conduct operations vary and our subsidiaries are frequently subjected to minimum taxation regimes. In some jurisdictions, tax liabilities are based on gross revenues, statutory or negotiated deemed profits or other factors, rather than on net income and our subsidiaries are frequently unable to realize tax benefits when they operate at a loss. Accordingly, during periods of declining profitability, our consolidated income tax expense generally does not decline proportionally with consolidated income, which results in higher effective income tax rates. Furthermore, we generally continue to incur income tax expense in periods in which we operate at a loss on a consolidated basis. Historically, we calculated our provision for income taxes during interim reporting periods by applying the estimated annual effective tax rate for the full fiscal year to pre-tax income or loss, excluding discrete items, for the reporting period. We determined that since small changes in estimated pre-tax income or loss would result in significant changes in the estimated annual effective tax rate, the historical method would not provide a reliable estimate of income taxes for the quarter ended March 31, 2019. We used a discrete effective tax rate method to calculate income taxes for the quarters ended March 31, 2019 and 2018. We will continue to evaluate income tax estimates under the historical method in subsequent quarters and employ a discrete effective tax rate method if warranted. Discrete income tax expense for the quarter ended March 31, 2019 was $0.6 million and was attributable to unrecognized tax benefits associated with tax positions taken in prior years. Discrete income tax benefit for the quarter ended March 31, 2018 was $8.9 million and was primarily attributable to U.S. tax reform and a restructuring transaction, partially offset by discrete tax expense related to the repurchase and redemption of senior notes and unrecognized tax benefits associated with tax positions taken in prior years.

Income Taxes

Ensco Rowan plc, our parent company, is domiciled and resident in the U.K. Our subsidiaries conduct operations and earn income in numerous countries and are subject to the laws of taxing jurisdictions within those countries. The income of our non-U.K. subsidiaries is generally not subject to U.K. taxation. Income tax rates imposed in the tax jurisdictions in which our subsidiaries conduct operations vary, as does the tax base to which the rates are applied. In some cases, tax rates may be applicable to gross revenues, statutory or negotiated deemed profits or other bases utilized under local tax laws, rather than to net income. Therefore, we generally incur income tax expense in periods in which we operate at a loss.

Our drilling rigs frequently move from one taxing jurisdiction to another to perform contract drilling services. In some instances, the movement of our drilling rigs among taxing jurisdictions will involve the transfer of ownership of the drilling rigs among our subsidiaries. As a result of frequent changes in the taxing jurisdictions in which our drilling rigs are operated and/or owned, changes in the overall level of our income and changes in tax laws, our consolidated effective income tax rate may vary substantially from one reporting period to another.

Income tax rates and taxation systems in the jurisdictions in which our subsidiaries conduct operations vary and our subsidiaries are frequently subjected to minimum taxation regimes. In some jurisdictions, tax liabilities are based on gross revenues, statutory or negotiated deemed profits or other factors, rather than on net income and our subsidiaries are frequently unable to realize tax benefits when they operate at a loss. Accordingly, during periods of declining profitability, our consolidated income tax expense generally does not decline proportionally with consolidated income, which results in higher effective income tax rates. Furthermore, we generally continue to incur income tax expense in periods in which we operate at a loss on a consolidated basis.

Historically, we calculated our provision for income taxes during interim reporting periods by applying the estimated annual effective tax rate for the full fiscal year to pre-tax income or loss, excluding discrete items, for the reporting period. We determined that since small changes in estimated pre-tax income or loss would result in significant changes in the estimated annual effective tax rate, the historical method would not provide a reliable estimate of income taxes for the quarter ended March 31, 2019. We used a discrete effective tax rate method to calculate income taxes for the quarters ended March 31, 2019 and 2018. We will continue to evaluate income tax estimates under the historical method in subsequent quarters and employ a discrete effective tax rate method if warranted.

Discrete income tax expense for the quarter ended March 31, 2019 was $0.6 million and was attributable to unrecognized tax benefits associated with tax positions taken in prior years. Discrete income tax benefit for the quarter ended March 31, 2018 was $8.9 million and was primarily attributable to U.S. tax reform and a restructuring transaction, partially offset by discrete tax expense related to the repurchase and redemption of senior notes and unrecognized tax benefits associated with tax positions taken in prior years.