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Fair Value (Available-For-Sale Securities) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Fair Value Disclosure [Line Items]
Amortized Cost	$ 134.5	$ 129.4
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	2.8	0.4
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(0.2)	(1.1)
Fair Value	137.1	128.7
U.S. Treasury securities
Fair Value Disclosure [Line Items]
Amortized Cost	37.4	33.7
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	0.9	0.1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0.0	(0.3)
Fair Value	38.3	33.5
Corporate/Other Debt Securities
Fair Value Disclosure [Line Items]
Amortized Cost	97.1	95.7
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	1.9	0.3
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(0.2)	(0.8)
Fair Value	$ 98.8	$ 95.2

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Fair Value Disclosure [Line Items]

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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