Summary of the status of the Company's share options and related information (Details) (Share options [Member], USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share options [Member]
Share Options
Outstanding at beginning of period (in shares)	5,611,000	9,116,000	13,919,000
Granted (in shares)	0	0	80,000
Exercised (in shares)	(2,116,000)	(3,413,000)	(4,546,000)
Forfeited and expired (in shares)	(33,000)	(92,000)	(337,000)
Outstanding at end of period (in shares)	3,462,000	5,611,000	9,116,000
Exercisable at end of period (in shares)	3,270,000	5,117,000	7,833,000
Shares available for grant (in shares)	11,330,000	17,024,000	24,508,000
Weighted-Average Exercise Price
Outstanding at beginning of period (in dollars per share)	$ 32	$ 32	$ 32
Granted (in dollars per share)	$ 0	$ 0	$ 53
Exercised (in dollars per share)	$ 32	$ 31	$ 32
Forfeited and expired (in dollars per share)	$ 34	$ 37	$ 36
Outstanding at end of period (in dollars per share)	$ 32	$ 32	$ 32
Exercisable at end of period (in dollars per share)	$ 32	$ 31	$ 30