Summary of Significant Accounting Policies (Policies)	3 Months Ended
Mar. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation: The condensed consolidated financial statements included in this report are unaudited and have been prepared in accordance with United States (“U.S.”) generally accepted accounting principles (“U.S. GAAP”) for interim financial reporting and U.S. Securities and Exchange Commission (“SEC”) regulations. The year-end condensed consolidated balance sheet data was derived from audited financial statements, but does not include all disclosures required by U.S. GAAP. Certain information and footnote disclosures normally included in annual financial statements prepared in accordance with U.S. GAAP have been condensed or omitted. In the opinion of management, these financial statements include all adjustments, which are of a normal recurring nature, necessary for a fair statement of the financial position, results of operations, cash flows and the change in equity for the periods presented. The condensed consolidated financial statements for the three months ended March 31, 2017 should be read in conjunction with the consolidated financial statements and notes thereto of West Pharmaceutical Services, Inc. and its majority-owned subsidiaries (which may be referred to as “West”, the “Company”, “we”, “us” or “our”) appearing in our Annual Report on Form 10-K for the year ended December 31, 2016 (the “2016 Annual Report”). The results of operations for any interim period are not necessarily indicative of results for the full year.
New Accounting Standards	Recently Adopted Standards In January 2017, the Financial Accounting Standards Board (“FASB”) issued guidance which removes the second step of the goodwill impairment test. A goodwill impairment charge will now be the amount by which a reporting unit's carrying amount exceeds its fair value, not to exceed the total amount of goodwill allocated to that reporting unit. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2019. Early adoption is permitted. We adopted this guidance as of January 1, 2017, on a prospective basis. The adoption did not have a material impact on our financial statements. In January 2017, the FASB issued guidance which clarifies the definition of a business to assist entities with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. We adopted this guidance as of January 1, 2017, on a prospective basis. The adoption did not have a material impact on our financial statements. In October 2016, the FASB issued guidance which requires companies to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. Early adoption is permitted. We adopted this guidance as of January 1, 2017, on a modified retrospective basis. As a result of the adoption, a cumulative-effect adjustment of $4.1 million was recorded within retained earnings in our condensed consolidated balance sheet as of January 1, 2017 for unamortized tax expense previously deferred and previously unrecognized deferred tax assets. In March 2016, the FASB issued guidance that simplifies several aspects of the accounting for share-based payment transactions, including income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. We adopted this guidance as of January 1, 2017, on a prospective basis as it relates to the timing or recognition and classification of share-based compensation award-related income tax effects. For the three months ended March 31, 2017, we recorded a tax benefit of $15.9 million within income tax expense in our condensed consolidated statement of income. These tax benefits were recorded within capital in excess of par value in our condensed consolidated balance sheet in the prior-year period. Also per the amended guidance, we classified the $15.9 million of excess tax benefits within net cash provided by operating activities in our condensed consolidated statement of cash flows, rather than net cash used in financing activities, which included the excess tax benefits for the three months ended March 31, 2016. The amended guidance allows entities to account for award forfeitures as they occur, however, we have elected to continue to estimate forfeitures expected to occur to determine the amount of compensation cost to be recognized in each period. We expect to record additional tax benefits throughout 2017. In March 2016, the FASB issued guidance that simplifies the transition to the equity method of accounting. This guidance eliminates the requirement to retroactively adopt the equity method of accounting when there is an increase in the level of ownership interest or degree of influence. We adopted this guidance as of January 1, 2017, on a prospective basis. The adoption did not have a material impact on our financial statements. In July 2015, the FASB issued guidance regarding the subsequent measurement of inventory. This guidance requires inventory measured using any method other than last-in, first-out or the retail inventory method to be measured at the lower of cost and net realizable value. Net realizable value represents estimated selling prices in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. We adopted this guidance as of January 1, 2017, on a prospective basis. The adoption did not have a material impact on our financial statements. Standards Issued Not Yet Adopted In March 2017, the FASB issued guidance on the presentation of net periodic pension and postretirement benefit cost (net benefit cost). The guidance requires the bifurcation of net benefit cost. The service cost component will be presented with other employee compensation costs in operating income (or capitalized in assets) and the other components will be reported separately outside of operations, and will not be eligible for capitalization. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. Early adoption is permitted. We are currently evaluating the impact that this guidance will have on our financial statements. In November 2016, the FASB issued guidance on the classification and presentation of restricted cash in the statement of cash flows. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. Early adoption is permitted. As of March 31, 2017, we had no restricted cash. In August 2016, the FASB issued guidance to reduce the diversity in how certain cash receipts and cash payments are presented and classified in the statement of cash flows. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. Early adoption is permitted. We are currently evaluating the impact that this guidance will have on our financial statements. In February 2016, the FASB issued guidance on the accounting for leases. This guidance requires lessees to recognize lease assets and lease liabilities on the balance sheet and to expand disclosures about leasing arrangements, both qualitative and quantitative. In terms of transition, the guidance requires adoption based upon a modified retrospective approach. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2018. We are currently evaluating the impact that this guidance will have on our financial statements. As of March 31, 2017, future minimum rental payments under non-cancelable operating leases were $65.8 million. In January 2016, the FASB issued guidance that addresses certain aspects of recognition, measurement, presentation, and disclosure of financial instruments. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. We believe that the adoption of this guidance will not have a material impact on our financial statements. In May 2014, the FASB issued guidance on the accounting for revenue from contracts with customers that will supersede most existing revenue recognition guidance, including industry-specific guidance. The core principle requires an entity to recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In addition, the guidance requires enhanced disclosures regarding the nature, timing and uncertainty of revenue and cash flows arising from an entity's contracts with customers. The FASB subsequently issued additional clarifying standards to address issues arising from implementation of the new revenue recognition standard. This guidance is effective for interim and annual reporting periods beginning on or after December 15, 2017. Early adoption is permitted as of one year prior to the current effective date. Entities can choose to apply the guidance using either a full retrospective approach or a modified retrospective approach. We have made progress towards completion of our evaluation of the potential impact that the adoption of this guidance will have on our financial statements.

Recently Adopted Standards

In January 2017, the Financial Accounting Standards Board (“FASB”) issued guidance which removes the second step of the goodwill impairment test. A goodwill impairment charge will now be the amount by which a reporting unit's carrying amount exceeds its fair value, not to exceed the total amount of goodwill allocated to that reporting unit. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2019. Early adoption is permitted. We adopted this guidance as of January 1, 2017, on a prospective basis. The adoption did not have a material impact on our financial statements.

In January 2017, the FASB issued guidance which clarifies the definition of a business to assist entities with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. We adopted this guidance as of January 1, 2017, on a prospective basis. The adoption did not have a material impact on our financial statements.

In October 2016, the FASB issued guidance which requires companies to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. Early adoption is permitted. We adopted this guidance as of January 1, 2017, on a modified retrospective basis. As a result of the adoption, a cumulative-effect adjustment of $4.1 million was recorded within retained earnings in our condensed consolidated balance sheet as of January 1, 2017 for unamortized tax expense previously deferred and previously unrecognized deferred tax assets.

In March 2016, the FASB issued guidance that simplifies several aspects of the accounting for share-based payment transactions, including income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. We adopted this guidance as of January 1, 2017, on a prospective basis as it relates to the timing or recognition and classification of share-based compensation award-related income tax effects. For the three months ended March 31, 2017, we recorded a tax benefit of $15.9 million within income tax expense in our condensed consolidated statement of income. These tax benefits were recorded within capital in excess of par value in our condensed consolidated balance sheet in the prior-year period. Also per the amended guidance, we classified the $15.9 million of excess tax benefits within net cash provided by operating activities in our condensed consolidated statement of cash flows, rather than net cash used in financing activities, which included the excess tax benefits for the three months ended March 31, 2016. The amended guidance allows entities to account for award forfeitures as they occur, however, we have elected to continue to estimate forfeitures expected to occur to determine the amount of compensation cost to be recognized in each period. We expect to record additional tax benefits throughout 2017.

In March 2016, the FASB issued guidance that simplifies the transition to the equity method of accounting. This guidance eliminates the requirement to retroactively adopt the equity method of accounting when there is an increase in the level of ownership interest or degree of influence. We adopted this guidance as of January 1, 2017, on a prospective basis. The adoption did not have a material impact on our financial statements.

In July 2015, the FASB issued guidance regarding the subsequent measurement of inventory. This guidance requires inventory measured using any method other than last-in, first-out or the retail inventory method to be measured at the lower of cost and net realizable value. Net realizable value represents estimated selling prices in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. We adopted this guidance as of January 1, 2017, on a prospective basis. The adoption did not have a material impact on our financial statements.

Standards Issued Not Yet Adopted

In March 2017, the FASB issued guidance on the presentation of net periodic pension and postretirement benefit cost (net benefit cost). The guidance requires the bifurcation of net benefit cost. The service cost component will be presented with other employee compensation costs in operating income (or capitalized in assets) and the other components will be reported separately outside of operations, and will not be eligible for capitalization. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. Early adoption is permitted. We are currently evaluating the impact that this guidance will have on our financial statements.

In November 2016, the FASB issued guidance on the classification and presentation of restricted cash in the statement of cash flows. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. Early adoption is permitted. As of March 31, 2017, we had no restricted cash.

In August 2016, the FASB issued guidance to reduce the diversity in how certain cash receipts and cash payments are presented and classified in the statement of cash flows. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. Early adoption is permitted. We are currently evaluating the impact that this guidance will have on our financial statements.

In February 2016, the FASB issued guidance on the accounting for leases. This guidance requires lessees to recognize lease assets and lease liabilities on the balance sheet and to expand disclosures about leasing arrangements, both qualitative and quantitative. In terms of transition, the guidance requires adoption based upon a modified retrospective approach. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2018. We are currently evaluating the impact that this guidance will have on our financial statements. As of March 31, 2017, future minimum rental payments under non-cancelable operating leases were $65.8 million.

In January 2016, the FASB issued guidance that addresses certain aspects of recognition, measurement, presentation, and disclosure of financial instruments. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. We believe that the adoption of this guidance will not have a material impact on our financial statements.

In May 2014, the FASB issued guidance on the accounting for revenue from contracts with customers that will supersede most existing revenue recognition guidance, including industry-specific guidance. The core principle requires an entity to recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In addition, the guidance requires enhanced disclosures regarding the nature, timing and uncertainty of revenue and cash flows arising from an entity's contracts with customers. The FASB subsequently issued additional clarifying standards to address issues arising from implementation of the new revenue recognition standard. This guidance is effective for interim and annual reporting periods beginning on or after December 15, 2017. Early adoption is permitted as of one year prior to the current effective date. Entities can choose to apply the guidance using either a full retrospective approach or a modified retrospective approach. We have made progress towards completion of our evaluation of the potential impact that the adoption of this guidance will have on our financial statements.