Commitments and contingencies - Narrative (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2016	Jun. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 31, 2020
Other Commitments [Line Items]
Supplemental Damages Royalty Rate	27.60%
Active Pharmaceutical Ingredient [Member]
Purchase Commitments, Fiscal Year Maturity
2020	$ 271			$ 271
2021	45			45
2022	22			22
2023	22			22
2024	14			14
Actual payments for purchases related to active pharmaceutical ingredients				529	$ 1,000	$ 1,700
Indenix [Member]
Other Commitments [Line Items]
Loss Contingency, Damages Awarded, Value		$ 2,540
Loss Contingency, Motion Invalidated For Past Damages, Value			$ 2,540
Juno [Member]
Other Commitments [Line Items]
Loss Contingency, Damages Awarded, Value	$ 585
Supplemental Damages Royalty Rate	27.60%
Supplemental Damages Royalty Rate High End	33.10%
Loss Contingency, Estimate of Possible Loss	$ 200			200
Minimum [Member] | Juno [Member]
Other Commitments [Line Items]
Loss Contingency, Estimate of Possible Loss	0			0
Maximum [Member] | Juno [Member]
Other Commitments [Line Items]
Loss Contingency, Estimate of Possible Loss	$ 1,600			$ 1,600
Additional purchase commitments resulting from contract amended in January 2020 [Member] | Subsequent Event [Member]
Purchase Commitments, Fiscal Year Maturity
Purchase Obligation							$ 220