Commitment and Contingencies - Additional Information (Detail) - USD ($)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies [Line Items]
Product liability insurance for individual losses in excess of accrual amount	$ 125,000,000	$ 125,000,000
Amounts in excess to be covered by third party insurance	$ 7,500,000	$ 7,500,000

Maximum amount self insured by the company for an individual product liability claim. Amounts in excess to be covered by third party insurance.

No definition available.

Name:	aos_ProductLiabilityIndividualClaimMaximumAmount
Namespace Prefix:	aos_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant