| **Cash and Marketable Securities (Tables)**                        | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
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| **Cash and Cash Equivalents [Abstract]**                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
| Schedule of Investment Components                                  | The components of our investments as of December 31, 2016 are as follows (in millions): Cash & Cash Equivalents Restricted Cash Restricted Marketable Securities TotalCash$40.5 $60.9 $— $101.4Equity securities— — 57.7 57.7Total$40.5 $60.9$57.7 $159.1The components of our investments as of December 31, 2015 are as follows (in millions): Cash & Cash Equivalents Restricted Cash Restricted Marketable Securities TotalCash$61.6 $45.9 $— $107.5Equity securities— — 56.2 56.2Total$61.6 $45.9 $56.2 $163.7 |
| Schedule of Restricted Cash                                        | As of December 31, 2016 and 2015, Restricted cash consisted of the following (in millions): As of December 31, 2016 2015Affiliate cash$22.9 $20.3Self-insured captive funds38.0 25.6Total restricted cash$60.9 $45.9                                                                                                                                                                                                                                                                                                                                                                                                                                                |
| Available-for-sale Securities Cost to Fair Value Reconciliation    | A summary of our restricted marketable securities as of December 31, 2015 is as follows (in millions): Cost Gross Unrealized Gains Gross Unrealized Losses Fair ValueEquity securities$58.3 $0.3 $(2.4) $56.2A summary of our restricted marketable securities as of December 31, 2016 is as follows (in millions): Cost Gross Unrealized Gains Gross Unrealized Losses Fair ValueEquity securities$59.6 $0.2 $(2.1) $57.7                                                                                                                                                                                             |
| Investment information related to restricted marketable securities | Investing information related to our restricted marketable securities is as follows (in millions): For the Year Ended December 31, 2016 2015 2014Proceeds from sales of restricted available-for-sale securities$— $— $—Proceeds from sales of nonrestricted available-for-sale securities$— $12.8 $2.7Gross realized gains$— $1.2 $0.5Gross realized losses$— $— $(0.1)                                                                                                                                                                                                                         |

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| - Definition
Tabular disclosure of the reconciliation of available-for-sale securities from cost basis to fair value.
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| - Definition
Tabular disclosure of the components of cash, cash equivalents, and investments.
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| - Definition
Tabular disclosure of the proceeds from sales of available-for-sale securities and the gross realized gains and gross realized losses that have been included in earnings as a result of those sales.
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| - Definition
Tabular disclosure of the cash and cash items which are restricted as to withdrawal or usage. The provisions of any restrictions are described in a note to the financial statements. 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.
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