Percentage of voting equity interests acquired at the acquisition date in the business combination.

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Carrying amount as of the balance sheet date of obligations due all related parties. For classified balance sheets, represents the current portion of such liabilities (due within one year or within the normal operating cycle if longer).

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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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This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

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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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Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

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Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

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Related party transactions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2018
Kirin-Amgen, Inc. (K-A) [Member]
Related Party Transaction [Line Items]
Percentage of voting interests acquired			50.00%
Kirin-Amgen [Member]
Related Party Transaction [Line Items]
Ownership interest (in percent) in related party	50.00%
Kirin-Amgen [Member] \| Noncurrent other assets [Member]
Related Party Transaction [Line Items]
Approximate carrying value of the company's equity method investment	$ 570.0
Kirin-Amgen [Member] \| Accrued liabilities [Member]
Related Party Transaction [Line Items]
Amount due to related party	80.0
Kirin-Amgen [Member] \| Selling, general and administrative [Member]
Related Party Transaction [Line Items]
Company's share of profits (losses) of related party	68.0	$ 58.0
Kirin-Amgen [Member] \| Cost of sales [Member]
Related Party Transaction [Line Items]
Royalties earned by related party from Amgen	221.0	239.0
Kirin-Amgen [Member] \| Other revenues [Member]
Related Party Transaction [Line Items]
Revenues earned by Amgen from related party	$ 28.0	$ 31.0