| **Fair Value Measurements - Carrying Amounts and Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Millions** | Dec. 31, 2016 | Dec. 31, 2015 |
|-------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| Other Notes Payable [Member] | Carrying Amount [Member]                                                                             |          |          |
| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**                                                   |          |          |
| Carrying amounts and estimated fair values of financial instruments                                                                 | $ 55.8        | $ 39.2        |
| Other Notes Payable [Member] | Estimated Fair Value [Member]                                                                        |          |          |
| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**                                                   |          |          |
| Carrying amounts and estimated fair values of financial instruments                                                                 | 55.8          | 39.2          |
| Revolving Credit Facility [Member] | Carrying Amount [Member]                                                                       |          |          |
| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**                                                   |          |          |
| Carrying amounts and estimated fair values of financial instruments                                                                 | 152.0         | 130.0         |
| Revolving Credit Facility [Member] | Estimated Fair Value [Member]                                                                  |          |          |
| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**                                                   |          |          |
| Carrying amounts and estimated fair values of financial instruments                                                                 | 152.0         | 130.0         |
| Letter of Credit [Member] | Carrying Amount [Member]                                                                                |          |          |
| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**                                                   |          |          |
| Carrying amounts and estimated fair values of financial instruments                                                                 | 0.0           | 0.0           |
| Letter of Credit [Member] | Estimated Fair Value [Member]                                                                           |          |          |
| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**                                                   |          |          |
| Carrying amounts and estimated fair values of financial instruments                                                                 | 33.3          | 34.2          |
| Term Loan Facilities [Member] | Term Loan Facilities [Member] | Carrying Amount [Member]                                            |          |          |
| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**                                                   |          |          |
| Carrying amounts and estimated fair values of financial instruments                                                                 | 421.2         | 443.3         |
| Term Loan Facilities [Member] | Term Loan Facilities [Member] | Estimated Fair Value [Member]                                       |          |          |
| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**                                                   |          |          |
| Carrying amounts and estimated fair values of financial instruments                                                                 | 422.5         | 445.0         |
| 7.75% Senior Notes Due 2022 [Member] | Senior Notes [Member] | Carrying Amount [Member]                                             |          |          |
| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**                                                   |          |          |
| Carrying amounts and estimated fair values of financial instruments                                                                 | 0.0           | 174.3         |
| 7.75% Senior Notes Due 2022 [Member] | Senior Notes [Member] | Estimated Fair Value [Member]                                        |          |          |
| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**                                                   |          |          |
| Carrying amounts and estimated fair values of financial instruments                                                                 | 0.0           | 183.7         |
| 5.125% Senior Notes Due 2023 [Member] | Senior Notes [Member] | Carrying Amount [Member]                                            |          |          |
| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**                                                   |          |          |
| Carrying amounts and estimated fair values of financial instruments                                                                 | 295.3         | 294.6         |
| 5.125% Senior Notes Due 2023 [Member] | Senior Notes [Member] | Estimated Fair Value [Member]                                       |          |          |
| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**                                                   |          |          |
| Carrying amounts and estimated fair values of financial instruments                                                                 | 297.8         | 288.0         |
| 5.75% Senior Notes Due 2024 [Member] | Senior Notes [Member] | Carrying Amount [Member]                                             |          |          |
| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**                                                   |          |          |
| Carrying amounts and estimated fair values of financial instruments                                                                 | 1,193.2       | 1,192.6       |
| 5.75% Senior Notes Due 2024 [Member] | Senior Notes [Member] | Estimated Fair Value [Member]                                        |          |          |
| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**                                                   |          |          |
| Carrying amounts and estimated fair values of financial instruments                                                                 | 1,216.6       | 1,146.0       |
| 5.75% Senior Notes Due 2025 [Member] | Senior Notes [Member] | Carrying Amount [Member]                                             |          |          |
| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**                                                   |          |          |
| Carrying amounts and estimated fair values of financial instruments                                                                 | 343.9         | 343.4         |
| 5.75% Senior Notes Due 2025 [Member] | Senior Notes [Member] | Estimated Fair Value [Member]                                        |          |          |
| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**                                                   |          |          |
| Carrying amounts and estimated fair values of financial instruments                                                                 | 349.6         | 332.5         |
| 2.00% Convertible Senior Subordinated Notes due 2043 [Member] | Senior Subordinated Notes [Member] | Carrying Amount [Member]       |          |          |
| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**                                                   |          |          |
| Carrying amounts and estimated fair values of financial instruments                                                                 | 275.7         | 265.9         |
| 2.00% Convertible Senior Subordinated Notes due 2043 [Member] | Senior Subordinated Notes [Member] | Estimated Fair Value [Member]  |          |          |
| **Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]**                                                   |          |          |
| Carrying amounts and estimated fair values of financial instruments                                                                 | $ 382.6       | $ 345.0       |

| 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_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.
+ References
No definition available.
+ Details**Name:**us-gaap_LongTermDebtFairValue**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_LongtermDebtTypeAxis=us-gaap_NotesPayableOtherPayablesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                       |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                                                    |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FairValueByMeasurementBasisAxis=us-gaap_EstimateOfFairValueFairValueDisclosureMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_CreditFacilityAxis=us-gaap_LetterOfCreditMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DebtInstrumentAxis=hls_TermLoanFacilitiesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_LongtermDebtTypeAxis=us-gaap_LoansPayableMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DebtInstrumentAxis=hls_SeniorNotes0775Due2022Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                              |
|------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorNotesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DebtInstrumentAxis=hls_SeniorNotes05.125Due2023Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DebtInstrumentAxis=hls_SeniorNotes0575Due2024Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DebtInstrumentAxis=hls_SeniorNotes05.75Due2025Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                           |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DebtInstrumentAxis=hls_A2.00ConvertibleSeniorSubordinatedNotesdue2043Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorSubordinatedNotesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |