| **Business Combinations - Table 3 (Details) (USD $)In Millions, unless otherwise specified** | 12 Months Ended                                                                                                                                                                             |                                                                                                                                                                                             |                       |                       |                       |
|----------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------|-----------------------|-----------------------|
||
| **Business Acquisition [Line Items]**                                                        |                                                                                                                                                                                        |                                                                                                                                                                                        |                  |                  |                  |
| Total current assets                                                                         |                                                                                                                                                                                        | $ 12.1us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssets                                                                                     |                  |                  |                  |
| Property and equipment, net                                                                  |                                                                                                                                                                                        | 36.9us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment                                                                           |                  |                  |                  |
| Goodwill                                                                                     | 1,084.0us-gaap_Goodwill                                                                                                                                                                     | 34.6us-gaap_Goodwill                                                                                                                                                                        | 456.9us-gaap_Goodwill | 437.3us-gaap_Goodwill | 421.7us-gaap_Goodwill |
| Total assets acquired                                                                        |                                                                                                                                                                                        | 99.8us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets                                                                                              |                  |                  |                  |
| Total current liabilities assumed                                                            |                                                                                                                                                                                        | (7.8)us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities                                                                                 |                  |                  |                  |
| Total long-term liabilities                                                                  |                                                                                                                                                                                        | (13.4)us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilities                                                                             |                  |                  |                  |
| Net assets acquired                                                                          |                                                                                                                                                                                        | 78.6us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet                                                                                                 |                  |                  |                  |
| Noncompete Agreements [Member]                                                               |                                                                                                                                                                                        |                                                                                                                                                                                        |                  |                  |                  |
| **Business Acquisition [Line Items]**                                                        |                                                                                                                                                                                        |                                                                                                                                                                                        |                  |                  |                  |
| Identifiable intangible assets                                                               | 5.6us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis= us-gaap_NoncompeteAgreementsMember | 0.4us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis= us-gaap_NoncompeteAgreementsMember |                  |                  |                  |
| Noncompete Agreements [Member] | Minimum [Member]                                            |                                                                                                                                                                                        |                                                                                                                                                                                        |                  |                  |                  |
| **Useful Lives of Acquired Finite-Lived Intangible Assets [Abstract]**                       |                                                                                                                                                                                        |                                                                                                                                                                                        |                  |                  |                  |
| Acquired Finite-lived Intangible Asset, Weighted Average Useful Life                         | 2 years                                                                                                                                                                                     |                                                                                                                                                                                        |                  |                  |                  |
| Noncompete Agreements [Member] | Maximum [Member]                                            |                                                                                                                                                                                        |                                                                                                                                                                                        |                  |                  |                  |
| **Useful Lives of Acquired Finite-Lived Intangible Assets [Abstract]**                       |                                                                                                                                                                                        |                                                                                                                                                                                        |                  |                  |                  |
| Acquired Finite-lived Intangible Asset, Weighted Average Useful Life                         | 3 years                                                                                                                                                                                     |                                                                                                                                                                                        |                  |                  |                  |
| Trade Names [Member]                                                                         |                                                                                                                                                                                        |                                                                                                                                                                                        |                  |                  |                  |
| **Business Acquisition [Line Items]**                                                        |                                                                                                                                                                                        |                                                                                                                                                                                        |                  |                  |                  |
| Identifiable intangible assets                                                               |                                                                                                                                                                                        | 2.9us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis= us-gaap_TradeNamesMember           |                  |                  |                  |
| **Useful Lives of Acquired Finite-Lived Intangible Assets [Abstract]**                       |                                                                                                                                                                                        |                                                                                                                                                                                        |                  |                  |                  |
| Acquired Finite-lived Intangible Asset, Weighted Average Useful Life                         | 20 years                                                                                                                                                                                    |                                                                                                                                                                                        |                  |                  |                  |
| Certificates of need [Member]                                                                |                                                                                                                                                                                        |                                                                                                                                                                                        |                  |                  |                  |
| **Business Acquisition [Line Items]**                                                        |                                                                                                                                                                                        |                                                                                                                                                                                        |                  |                  |                  |
| Identifiable intangible assets                                                               |                                                                                                                                                                                        | 10.8us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis= hls_CertificateOfNeedMember       |                  |                  |                  |
| **Useful Lives of Acquired Finite-Lived Intangible Assets [Abstract]**                       |                                                                                                                                                                                        |                                                                                                                                                                                        |                  |                  |                  |
| Acquired Finite-lived Intangible Asset, Weighted Average Useful Life                         | 20 years                                                                                                                                                                                    |                                                                                                                                                                                        |                  |                  |                  |
| License [Member]                                                                             |                                                                                                                                                                                        |                                                                                                                                                                                        |                  |                  |                  |
| **Business Acquisition [Line Items]**                                                        |                                                                                                                                                                                        |                                                                                                                                                                                        |                  |                  |                  |
| Identifiable intangible assets                                                               | 58.2us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis= hls_LicenseMember                 | $ 2.1us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis= hls_LicenseMember                |                  |                  |                  |
| **Useful Lives of Acquired Finite-Lived Intangible Assets [Abstract]**                       |                                                                                                                                                                                        |                                                                                                                                                                                        |                  |                  |                  |
| Acquired Finite-lived Intangible Asset, Weighted Average Useful Life                         | 20 years                                                                                                                                                                                    |                                                                                                                                                                                        |                  |                  |                  |

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Amount of liabilities due within one year or within the normal operating cycle, if longer, assumed at the acquisition date.
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The amount of identifiable intangible assets recognized as of the acquisition date.
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Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.
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Amount of liabilities due after one year or the normal operating cycle, if longer, assumed at the acquisition date.
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The amount of property, plant, and equipment recognized as of the acquisition date.
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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.
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