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Debt Securities - Gross Unrealized Losses and Fair Value Available-For-Sale Investments in Unrealized Loss Position (Detail) - Corporate debt securities
$ in Millions
Dec. 31, 2019
USD ($)
Debt Securities, Available-for-sale [Line Items]  
Less Than 12 Months, Fair Value $ 186.1
Less Than 12 Months, Unrealized Loss (0.1)
12 Months or Longer, Fair Value 0.0
12 Months or Longer, Unrealized Loss 0.0
Total Fair Value 186.1
Total Unrealized Loss $ (0.1)