Quarterly financial data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 3,717	$ 4,261	$ 4,017	$ 3,789	$ 3,750	$ 4,116	$ 3,693	$ 3,402	$ 15,784	$ 14,961	$ 13,370
Gross profit	2,407	2,804	2,619	2,447	2,440	2,656	2,374	2,144	10,277	9,614	8,257
Acquisition charges	79	80	79	80	79	80	79	80	318	318	319
Restructuring charges/other	(2)	1	3	1	3	1	3	4	3	11	(15)
Operating profit	1,516	1,937	1,712	1,548	1,563	1,788	1,480	1,252	6,713	6,083	4,855
Net income	$ 1,239	$ 1,570	$ 1,405	$ 1,366	$ 344	$ 1,285	$ 1,056	$ 997	$ 5,580	$ 3,682	$ 3,595
Basic earnings per common share	$ 1.29	$ 1.61	$ 1.43	$ 1.38	$ 0.35	$ 1.29	$ 1.05	$ 0.99	$ 5.71	$ 3.68	$ 3.54
Diluted earnings per common share	$ 1.27	$ 1.58	$ 1.40	$ 1.35	$ 0.34	$ 1.26	$ 1.03	$ 0.97	$ 5.59	$ 3.61	$ 3.48