Quarterly financial data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 3,414	$ 3,675	$ 3,273	$ 3,008	$ 3,189	$ 3,429	$ 3,232	$ 3,150	$ 13,370	$ 13,000	$ 13,045
Gross profit	2,133	2,280	2,003	1,824	1,866	1,997	1,881	1,816	8,240	7,560	7,427
Acquisition charges	80	80	79	80	81	83	82	83	319	329	330
Restructuring charges/other	(20)	1	2	2	(68)	0	(1)	(2)	(15)	(71)	(51)
Operating profit	1,319	1,395	1,117	968	1,142	1,164	1,010	958	4,799	4,274	3,947
Net income	$ 1,047	$ 1,018	$ 819	$ 711	$ 836	$ 798	$ 696	$ 656	$ 3,595	$ 2,986	$ 2,821
Basic earnings per common share	$ 1.04	$ 1.00	$ 0.81	$ 0.70	$ 0.81	$ 0.77	$ 0.66	$ 0.62	$ 3.54	$ 2.86	$ 2.61
Diluted earnings per common share	$ 1.02	$ 0.98	$ 0.79	$ 0.69	$ 0.80	$ 0.76	$ 0.65	$ 0.61	$ 3.48	$ 2.82	$ 2.57