Shareholders' equity (Detail) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019 SFr / shares shares	Apr. 30, 2019 $ / shares	Apr. 30, 2018 $ / shares	Apr. 30, 2017 $ / shares	Nov. 21, 2019 USD ($)	May 31, 2019 $ / shares	Dec. 31, 2018 SFr / shares shares	Dec. 01, 2018 USD ($)	May 31, 2018 $ / shares	Dec. 31, 2017 shares	Dec. 21, 2017 USD ($)	May 31, 2017 $ / shares	Dec. 31, 2016 shares	Nov. 30, 2016 USD ($)
Stockholders' Equity Note [Abstract]
Dividend installments | $ / shares		$ 0.75	$ 0.73	$ 0.71
The number of votes associated with one Common Share	one
The maximum ownership percentage for voting allowed for any one shareholder	10.00%
Annual dividend per share approved by shareholders | $ / shares						$ 3.00			$ 2.92			$ 2.84
Authorized Share Capital [Line Items]
Common Shares, par value | SFr / shares	SFr 24.15						SFr 24.15
Document Period End Date	Dec. 31, 2019
Common Shares, shares issued | shares	479,783,864						479,783,864			479,783,864			479,783,864
General Purpose
Authorized Share Capital [Line Items]
Authorized share capital for future issuance | shares	200,000,000
Issuance of Debt
Authorized Share Capital [Line Items]
Authorized share capital for future issuance | shares	33,000,000
Employee Benefit Plans
Authorized Share Capital [Line Items]
Authorized share capital for future issuance | shares	25,410,929
Nov 2016 Stock Repurchase Plan [Member]
Authorized Share Capital [Line Items]
Stock repurchase program authorized amount | $														$ 1,000
2018 Stock Repurchase Plan [Member] [Domain]
Authorized Share Capital [Line Items]
Stock repurchase program authorized amount | $											$ 1,000
2019 Stock Repurchase Plan [Member]
Authorized Share Capital [Line Items]
Stock repurchase program authorized amount | $								$ 1,500
Nov 2019 Stock Repurchase Plan [Member]
Authorized Share Capital [Line Items]
Stock repurchase program authorized amount | $					$ 1,500