XML 92 R77.htm IDEA: XBRL DOCUMENT v3.8.0.1

Fair Value Measurement of Plan Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	$ 873.8	$ 785.6
Non-investment plan assets	1.0	1.4
Total plan assets	874.8	787.0
Short-term Investments
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	15.8	28.7
Equity Securities | Commingled Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	121.5	105.6
Equity Securities | Common Stock
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	220.3	254.0
Fixed Income Securities | Other Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	219.9	102.6
Fixed Income Securities | Commingled Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	99.8	90.3
Fixed Income Securities | US Treasury Securities
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	46.0	97.6
Other Investments | Private equity
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	20.9	28.0
Other Investments | Mutual Fund
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	51.8	4.5
Other Investments | Real estate funds
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	77.8	74.3
Quoted Prices In Active Markets For Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	268.3	352.7
Quoted Prices In Active Markets For Identical Assets (Level 1) | Short-term Investments
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	2.0	1.1
Quoted Prices In Active Markets For Identical Assets (Level 1) | Equity Securities | Common Stock
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	220.3	254.0
Quoted Prices In Active Markets For Identical Assets (Level 1) | Fixed Income Securities | US Treasury Securities
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	46.0	97.6
Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	506.8	310.9
Significant Other Observable Inputs (Level 2) | Short-term Investments
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	13.8	7.9
Significant Other Observable Inputs (Level 2) | Equity Securities | Commingled Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	121.5	105.6
Significant Other Observable Inputs (Level 2) | Fixed Income Securities | Other Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	219.9	102.6
Significant Other Observable Inputs (Level 2) | Fixed Income Securities | Commingled Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	99.8	90.3
Significant Other Observable Inputs (Level 2) | Other Investments | Mutual Fund
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	51.8	4.5
Significant Non-observable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	98.7	122.0	$ 117.6
Significant Non-observable Inputs (Level 3) | Short-term Investments
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments		19.7	12.4
Significant Non-observable Inputs (Level 3) | Real estate funds
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	77.8	74.3	$ 70.9
Significant Non-observable Inputs (Level 3) | Other Investments | Private equity
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	20.9	28.0
Significant Non-observable Inputs (Level 3) | Other Investments | Real estate funds
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan asset investments	$ 77.8	$ 74.3

X

- Definition

Defined benefit plan fair value of non-investment plan assets.

+ References

No definition available.

+ Details

Name:	aos_DefinedBenefitPlanFairValueOfNonInvestmentPlanAssets
Namespace Prefix:	aos_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Defined Benefit Plan Fair Value of Plan Assets Including Non-Investment Plan Assets

+ References

No definition available.

+ Details

Name:	aos_DefinedBenefitPlanFairValueOfPlanAssetsIncludingNoninvestmentPlanAssets
Namespace Prefix:	aos_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_ShortTermInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementClassOfStockAxis=aos_CommingledEquityFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CommonStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_FixedIncomeSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementClassOfStockAxis=aos_OtherFixedIncomeSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementClassOfStockAxis=aos_CommingledFixedIncomeFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementClassOfStockAxis=aos_PrivateEquityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_MutualFundMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_RealEstateFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: