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Commitment and Contingencies - Additional Information (Detail) - USD ($) | 12 Months Ended
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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

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- Definition Commitments and Contingencies [Line Items] + References No definition available. + Details
Name: | aos_CommitmentsAndContingenciesLineItems
Namespace Prefix: | aos_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Maximum aggregate amount of third party product liability insurance coverage for individual losses in excess of a specified amount. + References No definition available. + Details
Name: | aos_MaximumAggregateProductLiabilityInsuranceCoverage
Namespace Prefix: | aos_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Maximum amount self insured by the company for an individual product liability claim. Amounts in excess to be covered by third party insurance. + References No definition available. + Details
Name: | aos_ProductLiabilityIndividualClaimMaximumAmount
Namespace Prefix: | aos_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant