| **Cash and Marketable Securities - Restricted Cash (Details) - USD ($) $ in Millions** | Dec. 31, 2016 | Dec. 31, 2015 |
|----------------------------------------------------------------------------------------|---------------|---------------|
| **Restricted Cash and Cash Equivalents Items [Line Items]**                            |          |          |
| Total restricted cash                                                                  | $ 60.9        | $ 45.9        |
| Affiliate cash [Member]                                                                |          |          |
| **Restricted Cash and Cash Equivalents Items [Line Items]**                            |          |          |
| Total restricted cash                                                                  | 22.9          | 20.3          |
| Self-insured captive funds [Member]                                                    |          |          |
| **Restricted Cash and Cash Equivalents Items [Line Items]**                            |          |          |
| Total restricted cash                                                                  | $ 38.0        | $ 25.6        |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The carrying amounts of cash and cash equivalent items which are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against short-term borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. For a classified balance sheet represents the current portion only (the noncurrent portion has a separate concept); there is a separate and distinct element for unclassified presentations.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.1) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682
+ Details**Name:**us-gaap_RestrictedCashAndCashEquivalentsAtCarryingValue**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| 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_RestrictedCashAndCashEquivalentsItemsLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis=hls_AffiliateCashMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                            |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsAxis=hls_SelfInsuredCaptiveFundsMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |