| **Revenue Recognition - Segment Sales Disaggregated by Major Product Line (Details) - USD ($) $ in Millions** | 3 Months Ended |
|---------------------------------------------------------------------------------------------------------------|----------------|
||
| **Disaggregation of Revenue [Line Items]**                                                                    |           |   |
| Net sales                                                                                                     | $ 978.8        | $ 966.4 |
| Operating Segments | North America                                                                            |           |   |
| **Disaggregation of Revenue [Line Items]**                                                                    |           |   |
| Net sales                                                                                                     | 766.3          | 752.7 |
| Operating Segments | Rest of World                                                                            |           |   |
| **Disaggregation of Revenue [Line Items]**                                                                    |           |   |
| Net sales                                                                                                     | 226.9          | 219.1 |
| Operating Segments | Rest of World | China                                                                    |           |   |
| **Disaggregation of Revenue [Line Items]**                                                                    |           |   |
| Net sales                                                                                                     | 200.6          | 190.2 |
| Operating Segments | Rest of World | All other Rest of World                                                  |           |   |
| **Disaggregation of Revenue [Line Items]**                                                                    |           |   |
| Net sales                                                                                                     | 26.3           | 28.9 |
| Operating Segments | Water heaters and related parts | North America                                          |           |   |
| **Disaggregation of Revenue [Line Items]**                                                                    |           |   |
| Net sales                                                                                                     | 648.3          | 637.3 |
| Operating Segments | Boilers and related parts | North America                                                |           |   |
| **Disaggregation of Revenue [Line Items]**                                                                    |           |   |
| Net sales                                                                                                     | 58.7           | 58.4 |
| Operating Segments | Water treatment products and related parts | North America                               |           |   |
| **Disaggregation of Revenue [Line Items]**                                                                    |           |   |
| Net sales                                                                                                     | 59.3           | 57.0 |
| Inter-segment                                                                                                 |           |   |
| **Disaggregation of Revenue [Line Items]**                                                                    |           |   |
| Net sales                                                                                                     | $ (14.4)       | $ (5.4) |

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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.
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Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.
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