Shareholders' equity (Detail)	12 Months Ended												12 Months Ended					2 Months Ended
	Dec. 31, 2014 USD ($)	Dec. 31, 2014 CHF	Dec. 31, 2013 USD ($)	Dec. 31, 2013 CHF	Dec. 31, 2012 USD ($)	Dec. 31, 2012 CHF	May 31, 2014 USD ($)	May 31, 2013 USD ($)	May 31, 2012 USD ($)	Dec. 31, 2014 General Purpose	Dec. 31, 2014 Issuance of Debt	Dec. 31, 2014 Employee Benefit Plans	Dec. 31, 2014 November 2013 Stock Repurchase Plan [Member] USD ($)	Dec. 31, 2013 November 2013 Stock Repurchase Plan [Member] USD ($)	Dec. 31, 2012 November 2013 Stock Repurchase Plan [Member] USD ($)	Nov. 30, 2013 November 2013 Stock Repurchase Plan [Member] USD ($)	Jan. 01, 2015 2015 Stock Repurchase Plan [Member] USD ($)	Feb. 26, 2015 Subsequent Event [Member] 2015 Stock Repurchase Plan [Member] USD ($)
Stockholders' Equity Note [Abstract]
Dividend installments	$ 0.65		$ 0.51		$ 0.49
Increase to dividend approved by shareholders in January	$ 0.12
Common shares in treasury, shares	14,172,726	14,172,726	3,038,477	3,038,477	2,510,878	2,510,878
Conditional Share Issuance, by Scenario [Line Items]
Common Shares, par value		24.77		27.04
Par Value Reduction	$ 2.46	2.27	$ 2.02	1.85	$ 1.47	1.38
Repurchase of outstanding common shares, shares													13,982,358	3,266,531	100,000			1,877,463
Cost of shares acquired													$ 1,449,000,000	$ 290,000,000	$ 7,000,000			$ 211,000,000
Authorized share capital for general purposes										140,000,000	33,000,000	25,410,929
Stock repurchase program authorized amount																2,000,000,000	1,500,000,000
Share repurchase authorization remaining																		$ 1,300,000,000
Dividends Declared From Additional Paid In Capital	$ 0.24	0.20	$ 0	0	$ 0.59	0.53
Annual dividend per share approved by shareholders							$ 2.60	$ 2.04	$ 1.96
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%
Dividends declared per common share	$ 2.70	2.47	$ 2.02	1.85	$ 2.06	1.91