Quarterly financial data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 3,750	$ 4,116	$ 3,693	$ 3,402	$ 3,414	$ 3,675	$ 3,273	$ 3,008	$ 14,961	$ 13,370	$ 13,000
Gross profit	2,440	2,656	2,374	2,144	2,137	2,284	2,007	1,829	9,614	8,257	7,575
Acquisition charges	79	80	79	80	80	80	79	80	318	319	329
Restructuring charges/other	3	1	3	4	(20)	1	2	2	11	(15)	(71)
Operating profit	1,563	1,788	1,480	1,252	1,332	1,408	1,131	984	6,083	4,855	4,322
Net income	$ 344	$ 1,285	$ 1,056	$ 997	$ 1,047	$ 1,018	$ 819	$ 711	$ 3,682	$ 3,595	$ 2,986
Basic earnings per common share	$ 0.35	$ 1.29	$ 1.05	$ 0.99	$ 1.04	$ 1.00	$ 0.81	$ 0.70	$ 3.68	$ 3.54	$ 2.86
Diluted earnings per common share	$ 0.34	$ 1.26	$ 1.03	$ 0.97	$ 1.02	$ 0.98	$ 0.79	$ 0.69	$ 3.61	$ 3.48	$ 2.82