Commitments and contingencies - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Commitments [Line Items]
Operating leases expense	$ 109	$ 84	$ 81
Active Pharmaceutical Ingredient [Member]
Purchase Commitments, Fiscal Year Maturity
2019	503
2020	54
2021	51
2022	30
2023	27
Actual payments for purchases related to active pharmaceutical ingredients	$ 1,000	$ 1,700	$ 2,000