Quarterly financial data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 3,189	$ 3,429	$ 3,232	$ 3,150	$ 3,269	$ 3,501	$ 3,292	$ 2,983	$ 13,000	$ 13,045	$ 12,205
Gross profit	1,866	1,997	1,881	1,816	1,895	2,044	1,881	1,607	7,560	7,427	6,364
Acquisition charges	81	83	82	83	82	83	82	83	329	330	341
Restructuring charges/other	(68)	0	(1)	(2)	(27)	(9)	(4)	(11)	(71)	(51)	(189)
Operating profit	1,142	1,164	1,010	958	1,100	1,175	982	690	4,274	3,947	2,832
Net income	$ 836	$ 798	$ 696	$ 656	$ 825	$ 826	$ 683	$ 487	$ 2,986	$ 2,821	$ 2,162
Basic earnings per common share	$ 0.81	$ 0.77	$ 0.66	$ 0.62	$ 0.78	$ 0.77	$ 0.63	$ 0.44	$ 2.86	$ 2.61	$ 1.94
Diluted earnings per common share	$ 0.80	$ 0.76	$ 0.65	$ 0.61	$ 0.76	$ 0.76	$ 0.62	$ 0.44	$ 2.82	$ 2.57	$ 1.91