Fair value measurements - Additional Information (Details)	12 Months Ended
Dec. 31, 2019
Fair Value Disclosures [Abstract]
Percentage of postretirement benefit plan assets comprised of pension plan assets (more than)	99.00%

Percentage of postretirement benefit plan assets in company's pension plan assets.

No definition available.

Name:	son_PercentageOfPostretirementBenefitPlanAssetsInCompanysPensionPlanAssets
Namespace Prefix:	son_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration