Property, plant and equipment - Narrative (Details) $ in Millions		3 Months Ended	12 Months Ended
	Dec. 10, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Property, plant and equipment
Gain on sale-leaseback			$ 136	$ 33
Operating lease right-of-use assets	$ 63		176
Operating lease liabilities			213
Building Sale		$ 68
Gain on sale of assets		$ 33	$ 136	$ 33
Number of buildings		1
Properties in Palo Alto, California
Property, plant and equipment
Net proceeds	280
Gain on sale-leaseback	$ 136