| **Fair Value Measurements - Financial Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Millions** | Dec. 31, 2016 | Dec. 31, 2015 |
|--------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                               |          |          |
| Current portion of restricted marketable securities                                                                            | $ 24.2        | $ 16.1        |
| Restricted marketable securities                                                                                               | 33.5          | 40.1          |
| Redeemable noncontrolling interests                                                                                            | 138.3         | 121.1         |
| Fair Value, Inputs, Level 1 [Member]                                                                                           |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                               |          |          |
| Current portion of restricted marketable securities                                                                            | 0.0           | 0.0           |
| Restricted marketable securities                                                                                               | 0.0           | 0.0           |
| Redeemable noncontrolling interests                                                                                            | 0.0           | 0.0           |
| Fair Value, Inputs, Level 2 [Member]                                                                                           |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                               |          |          |
| Current portion of restricted marketable securities                                                                            | 24.2          | 16.1          |
| Restricted marketable securities                                                                                               | 33.5          | 40.1          |
| Redeemable noncontrolling interests                                                                                            | 0.0           | 0.0           |
| Fair Value, Inputs, Level 3 [Member]                                                                                           |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                               |          |          |
| Current portion of restricted marketable securities                                                                            | 0.0           | 0.0           |
| Restricted marketable securities                                                                                               | 0.0           | 0.0           |
| Redeemable noncontrolling interests                                                                                            | $ 138.3       | $ 121.1       |

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| - 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.
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| - Definition
Total debt and equity financial instruments including: (1) securities held-to-maturity, (2) trading securities, and (3) securities available-for-sale which are intended to be held for less than one year or the normal operating cycle, whichever is longer and that are pledged to one or more secured parties who have the right to buy, sell, or re-pledge the collateral.
+ References
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| - Definition
Total debt and equity financial instruments including: (1) securities held-to-maturity, (2) trading securities, and (3) securities available-for-sale which are intended to be held for greater than one year or the normal operating cycle, whichever is longer and that are pledged to one or more secured parties who have the right to buy, sell, or re-pledge the collateral.
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| - Definition
The aggregate fair value as of the reporting date of all noncontrolling interests which are redeemable by the (parent) entity (1) at a fixed or determinable price on a fixed or determinable date, (2) at the option of the holder of the noncontrolling interest, or (3) upon occurrence of an event that is not solely within the control of the (parent) entity. This item includes noncontrolling interest holder's ownership (or holders' ownership) regardless of the type of equity interest (common, preferred, other) including all potential organizational (legal) forms of the investee entity.
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