Fair value measurements Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gain on investment of equity securities	$ 115,000,000
In-process research and development impairment	820,000,000	$ 0	$ 432,000,000
Indefinite-lived Intangible Assets (Excluding Goodwill)	0
Fair value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term and long-term debt	27,100,000,000	35,500,000,000
Fair Value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term and long-term debt	$ 27,300,000,000	$ 33,500,000,000