|**Fair Value Measurements (Tables)**                                          | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
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|**Fair Value Disclosures [Abstract]**                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Schedule of Fair Value, Assets and Liabilities Measured on a Recurring Basis  | Our financial assets and liabilities that are measured at fair value on a recurring basis are as follows (in millions):Fair Value Measurements at Reporting Date UsingAs of March 31, 2018Fair ValueQuoted Prices in Active Markets for Identical Assets(Level 1)Significant Other Observable Inputs(Level 2)Significant Unobservable Inputs(Level 3)Valuation Technique(1)Other current assets:Current portion of restricted marketable securities$10.2$—$10.2$—MOther long-term assets:Restricted marketable securities45.9—45.9—MRedeemable noncontrolling interests198.6——198.6IAs of December 31, 2017Other current assets:Current portion of restricted marketable securities$17.8$—$17.8$—MOther long-term assets:Restricted marketable securities44.2—44.2—MRedeemable noncontrolling interests220.9——220.9I(1)The three valuation techniques are: market approach (M), cost approach (C), and income approach (I).
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|As of March 31, 2018                                                          | Fair Value                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Other current assets:                                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Current portion of restricted marketable securities                           | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Other long-term assets:                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Restricted marketable securities                                              | 45.9                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Redeemable noncontrolling interests                                           | 198.6                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|As of December 31, 2017                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Other current assets:                                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Current portion of restricted marketable securities                           | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Other long-term assets:                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Restricted marketable securities                                              | 44.2                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Redeemable noncontrolling interests                                           | 220.9                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Schedule of Carrying Amounts and Estimated Fair Values, Financial Instruments | The carrying amounts and estimated fair values for all of our other financial instruments are presented in the following table (in millions):As of March 31, 2018As of December 31, 2017Carrying AmountEstimated Fair ValueCarrying AmountEstimated Fair ValueLong-term debt:Advances under revolving credit facility$95.0$95.0$95.0$95.0Term loan facilities291.0292.5294.7296.35.125% Senior Notes due 2023296.1304.5295.9306.85.75% Senior Notes due 20241,194.11,221.01,193.91,228.55.75% Senior Notes due 2025344.6359.2344.4364.9Other notes payable87.987.982.382.3Financial commitments:Letters of credit—37.2—35.4                                                                                                                                                                                                                                                                                                
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|                                                                              | As of March 31, 2018                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|                                                                              | Carrying Amount                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Long-term debt:                                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Advances under revolving credit facility                                      | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Term loan facilities                                                          | 291.0                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|5.125% Senior Notes due 2023                                                  | 296.1                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|5.75% Senior Notes due 2024                                                   | 1,194.1                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    
|5.75% Senior Notes due 2025                                                   | 344.6                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Other notes payable                                                           | 87.9                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Financial commitments:                                                        |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Letters of credit                                                             | —                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          

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