Shareholders' equity (Detail) $ / shares in Units, $ in Millions	2 Months Ended	4 Months Ended	12 Months Ended
	Feb. 24, 2017 USD ($) shares	Apr. 30, 2014 $ / shares	Apr. 30, 2017 $ / shares	Dec. 31, 2016 USD ($) shares	Apr. 30, 2016 $ / shares	Dec. 31, 2015 USD ($) shares	Apr. 30, 2015 $ / shares	Dec. 31, 2014 USD ($) shares	Apr. 30, 2014 $ / shares	Dec. 31, 2016 SFr / shares shares	Nov. 30, 2016 USD ($)	May 31, 2016 $ / shares	Dec. 31, 2015 SFr / shares	May 31, 2015 $ / shares	Nov. 30, 2014 USD ($)	May 31, 2014 $ / shares	Nov. 30, 2013 USD ($)
Stockholders' Equity Note [Abstract]
Dividend installments | $ / shares		$ 0.63	$ 0.69		$ 0.67		$ 0.65		$ 0.51
Increase to dividend approved by shareholders in January | $ / shares		$ 0.12
The number of votes associated with one Common Share				1
The maximum ownership percentage for voting allowed for any one shareholder										10.00%
Annual dividend per share approved by shareholders | $ / shares												$ 2.76		$ 2.68		$ 2.60
Authorized Share Capital [Line Items]
Stock repurchase program authorized amount | $											$ 1,000				$ 1,500		$ 2,000
Common Shares, par value | SFr / shares										SFr 24.15			SFr 24.15
General Purpose
Authorized Share Capital [Line Items]
Authorized share capital for future issuance										200,000,000
Issuance of Debt
Authorized Share Capital [Line Items]
Authorized share capital for future issuance										33,000,000
Employee Benefit Plans
Authorized Share Capital [Line Items]
Authorized share capital for future issuance										25,410,929
Nov 2016 Stock Repurchase Plan [Member]
Authorized Share Capital [Line Items]
Treasury Stock, Shares, Acquired				0		6,677,663		13,982,358
Treasury Stock, Value, Acquired, Cost Method | $				$ 0		$ 734		$ 1,449
Nov 2016 Stock Repurchase Plan [Member] | Subsequent Event [Member]
Authorized Share Capital [Line Items]
Stock Repurchase Program, Remaining Authorized Repurchase Amount | $	$ 945
Treasury Stock, Shares, Acquired	419,623
Treasury Stock, Value, Acquired, Cost Method | $	$ 55