Quarterly financial data (unaudited) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 3,269	$ 3,501	$ 3,292	$ 2,983	$ 3,028	$ 3,244	$ 3,047	$ 2,885	$ 13,045	$ 12,205	$ 12,825
Gross profit	1,895	2,044	1,881	1,607	1,640	1,779	1,570	1,374	7,427	6,364	6,368
Acquisition charges	82	83	82	83	84	86	86	86	330	341	450
Restructuring charges/other	(27)	(9)	(4)	(11)	62	16	(282)	15	(51)	(189)	264
Operating profit	1,100	1,175	982	690	687	844	906	395	3,947	2,832	1,973
Net income	$ 825	$ 826	$ 683	$ 487	$ 511	$ 629	$ 660	$ 362	$ 2,821	$ 2,162	$ 1,759
Basic earnings per common share	$ 0.78	$ 0.77	$ 0.63	$ 0.44	$ 0.46	$ 0.56	$ 0.59	$ 0.32	$ 2.61	$ 1.94	$ 1.53
Diluted earnings per common share	$ 0.76	$ 0.76	$ 0.62	$ 0.44	$ 0.46	$ 0.56	$ 0.58	$ 0.32	$ 2.57	$ 1.91	$ 1.51