Commitment and contingencies - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other Commitments [Line Items]
Operating leases expense	$ 81	$ 78	$ 66
Active Pharmaceutical Ingredient [Member]
Purchase Commitments, Fiscal Year Maturity
2017	1,100
2018	345
2019	59
2020	20
2021	20
Actual payments for purchases related to active pharmaceutical ingredients	$ 2,000	$ 2,200	$ 1,800