| **Cover Page**                              | Apr. 12, 2022                            |
|---------------------------------------------|------------------------------------------|
| **Cover [Abstract]**                        |                                     |
| Document Type                               | 8-K                                      |
| Document Period End Date                    | Apr. 12,  2022                           |
| Entity Registrant Name                      | A. O. Smith Corporation                  |
| Entity Incorporation, State or Country Code | DE                                       |
| Entity File Number                          | 1-475                                    |
| Entity Tax Identification Number            | 39-0619790                               |
| Entity Address, Address Line One            | 11270 West Park Place                    |
| Entity Address, City or Town                | Milwaukee                                |
| Entity Address, State or Province           | WI                                       |
| Entity Address, Postal Zip Code             | 53224                                    |
| City Area Code                              | 414                                      |
| Local Phone Number                          | 359-4000                                 |
| Written Communications                      | false                                    |
| Soliciting Material                         | false                                    |
| Pre-commencement Tender Offer               | false                                    |
| Pre-commencement Issuer Tender Offer        | false                                    |
| Title of 12(b) Security                     | Common Stock (par value $1.00 per share) |
| Trading Symbol                              | AOS                                      |
| Security Exchange Name                      | NYSE                                     |
| Entity Emerging Growth Company              | false                                    |
| Entity Central Index Key                    | 0000091142                               |
| Amendment Flag                              | false                                    |

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Local phone number for entity.
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