XML 16 R1.htm IDEA: XBRL DOCUMENT v3.8.0.1
Document and Entity Information - USD ($)
 12 Months Ended
Dec. 31, 2017
Feb. 12, 2018
Jun. 30, 2017
Document Information [Line Items]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2017    
Document Fiscal Year Focus 2017    
Document Fiscal Period Focus FY    
Trading Symbol AOS    
Entity Registrant Name SMITH A O CORP    
Entity Central Index Key 0000091142    
Current Fiscal Year End Date --12-31    
Entity Well-known Seasoned Issuer Yes    
Entity Current Reporting Status Yes    
Entity Voluntary Filers No    
Entity Filer Category Large Accelerated Filer    
Common Class A      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding   26,065,195  
Entity Public Float     $ 54,942,874
Common Stock      
Document Information [Line Items]      
Entity Common Stock, Shares Outstanding   145,446,771  
Entity Public Float     $ 8,057,328,456