Share-based compensation (Rollforward Of Company's Stock Options) (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Number of Options [Roll Forward]
Number of option outstanding, beginning of period	10,579,507	11,942,893	11,483,104
Number of options granted	1,462,103	1,649,824	2,094,227
Number of options exercised	(2,401,869)	(2,741,238)	(1,328,715)
Number of options forfeited	(190,082)	(271,972)	(305,723)
Number of option outstanding, end of period	9,449,659	10,579,507	11,942,893
Number of options exercisable, December 31, 2012	6,446,407
Weighted-Average Exercise Price [Roll Forward]
Weighted-average exercise price of options outstanding, beginning of period (US$ oer share)	$ 49.78	$ 46.80	$ 45.46
Weighted-average exercise price of options granted (US$ per share)	$ 73.36	$ 62.68	$ 50.38
Weighted-average exercise price of options exercised (US$ per share)	$ 42.50	$ 44.45	$ 40.11
Weighted average exercise price of options forfeited (US$ per share)	$ 61.87	$ 51.33	$ 49.77
Weighted-average exercise price of options outstanding, end of period (US$ oer share	$ 55.03	$ 49.78	$ 46.80
Weighted average exercise price of options exercisable, December 31, 2012 (US$ per share)	$ 50.26
Options, Weighted-Average Fair Value and Total Intrinsic Value [Abstract]
Weighted-average fair value of stock options granted (US$ per share)	$ 15.58	$ 14.67	$ 12.09
Total intrinsic value of options exercised	$ 78	$ 63	$ 22
Total intrinsic value of options outstanding	234
Total intrinsic value of options exercisable, December 31, 2012	$ 190