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Investments in Affiliates and Other Related Party Transactions - Amounts Recorded in Consolidated Balance Sheet for Affiliates (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Equity Method Investments and Joint Ventures [Abstract]    
Aggregate investment in affiliates $ 146.5 $ 153.5
Receivables due from affiliates (including notes and advances) 140.7 121.8
Payables due to affiliates $ 0.2 $ 4.3