Shareholders' equity (Detail) In Millions, except Share data, unless otherwise specified	12 Months Ended									1 Months Ended
	Dec. 31, 2012 USD ($)	Dec. 31, 2012 CHF	Dec. 31, 2011 USD ($)	Dec. 31, 2011 CHF	Dec. 31, 2010 USD ($)	Dec. 31, 2010 CHF	Dec. 31, 2012 General Purpose	Dec. 31, 2012 Issuance of Debt	Dec. 31, 2012 Employee Benefit Plans	Aug. 31, 2011 November 2010 Stock Repurchase Plan [Member] USD ($)	Nov. 30, 2010 November 2010 Stock Repurchase Plan [Member] USD ($)
Stockholders' Equity Note [Abstract]
Dividend installments	$ 0.47		$ 0.35
Common shares in treasury, shares	2,510,878	2,510,878	5,905,136	5,905,136	6,151,707	6,151,707
Conditional Share Issuance, by Scenario [Line Items]
Repurchase of outstanding common shares, shares	100,000	100,000	2,058,860	2,058,860	4,926,082	4,926,082
Cost of shares acquired	$ 7		$ 132		$ 303
Authorized share capital for general purposes							140,000,000	33,000,000	25,410,929
Stock repurchase program authorized amount										303	600
Share repurchase authorization remaining	$ 461									$ 197
The number of votes associated with one Common Share	1	1
The maximum ownership percentage for voting allowed for any one shareholder	10.00%	10.00%
Par value reduction per common share		1.38		0.30
Dividends declared per common share	$ 2.06	1.91	$ 1.38	1.22	$ 1.30	1.31