XML 93 R78.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Reconciliation of Fair Value Measurements Using Significant Unobservable Inputs (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items] |  |
Plan assets at beginning of year | $ 785.6 |
Plan assets at end of year | 873.8 | $ 785.6
Significant Non-observable Inputs (Level 3) |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan assets at beginning of year | 122.0 | 117.6
Relating to assets still held at the reporting date | (2.1) | (2.1)
Relating to assets sold during the period | 7.8 | 9.3
Purchases, sales and settlements | (29.0) | (2.8)
Plan assets at end of year | 98.7 | 122.0
Short-term Investments |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan assets at beginning of year | 28.7 |
Plan assets at end of year | 15.8 | 28.7
Short-term Investments | Significant Non-observable Inputs (Level 3) |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan assets at beginning of year | 19.7 | 12.4
Purchases, sales and settlements | (19.7) | 7.3
Plan assets at end of year |  | 19.7
Real estate funds | Significant Non-observable Inputs (Level 3) |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan assets at beginning of year | 74.3 | 70.9
Relating to assets still held at the reporting date | 3.5 | 3.4
Plan assets at end of year | 77.8 | 74.3
Private equity | Significant Non-observable Inputs (Level 3) |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Plan assets at beginning of year | 28.0 | 34.3
Relating to assets still held at the reporting date | (5.6) | (5.5)
Relating to assets sold during the period | 7.8 | 9.3
Purchases, sales and settlements | (9.3) | (10.1)
Plan assets at end of year | $ 20.9 | $ 28.0

X
- Definition Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets sold. + 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 (d)(5)(iv)(02)(A) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsSoldDuringPeriod
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets still held. + 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 (d)(5)(iv)(02)(A) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsStillHeld
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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
- Definition Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from purchases, sales and settlements. + 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 (d)(5)(iv)(02)(B) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanPurchasesSalesAndSettlements
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_ShortTermInvestmentsMember
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_InvestmentTypeAxis=aos_PrivateEquityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |