Stock compensation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Stock compensation
Stock compensation expense	$ 46.3	$ 40.6	$ 88.8	$ 81.2
Stock Compensation Expense Capitalized	0.1	0.1	$ 0.3	0.2
Assumed annualized forfeiture rate (as a percent)			5.00%
Weighted-average fair value assumptions
Valuation method			Black-Scholes valuation model
Research and Development Expense
Stock compensation
Stock compensation expense	32.5	27.6	$ 61.2	55.0
Selling, General and Administrative Expenses
Stock compensation
Stock compensation expense	13.6	12.8	27.1	25.8
Cost of product revenues
Stock compensation
Stock compensation expense	$ 0.2	$ 0.2	$ 0.5	$ 0.4
Stock Options
Weighted-average fair value assumptions
Average risk-free interest rates (as a percent)	0.33%	2.26%	1.32%	2.49%
Average expected life (in years)	5 years 5 months 23 days	5 years 6 months 18 days	4 years 9 months 18 days	5 years 4 months 2 days
Volatility (as a percent)	39.00%	39.00%	40.00%	45.00%
Weighted-average fair value (in dollars per share)	$ 34.13	$ 30.92	$ 29.49	$ 31.47
Unrecognized compensation
Unrecognized compensation cost for nonvested option (in dollars)	$ 79.9		$ 79.9
Vesting period of recognition of the unrecognized compensation cost of nonvested awards			1 year 3 months 18 days
Restricted Stock Units (RSUs)
Weighted-average fair value assumptions
Average risk-free interest rates (as a percent)	0.16%	1.75%	0.19%	2.10%
Average expected life (in years)	6 months	6 months	6 months	6 months
Volatility (as a percent)	38.00%	37.00%	48.00%	34.00%
Weighted-average fair value (in dollars per share)	$ 19.50	$ 13.11	$ 17.47	$ 13.69
Unrecognized compensation
Unrecognized compensation cost for nonvested option (in dollars)	$ 77.9		$ 77.9
Vesting period of recognition of the unrecognized compensation cost of nonvested awards			1 year 7 months 6 days
Performance Stock Units (PSUs)
Unrecognized compensation
Unrecognized compensation cost for nonvested option (in dollars)	$ 21.4		$ 21.4
Vesting period of recognition of the unrecognized compensation cost of nonvested awards			1 year 6 months

Represents the expected annualized forfeiture rate for options granted.

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Represents the amount of stock compensation expenses capitalized.

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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Description of method used to estimate fair value of award under share-based payment arrangement.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Expected term of award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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