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Fair Value (Available-For-Sale Securities) (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Fair Value Disclosure [Line Items]
Amortized Cost	$ 128.6	$ 133.7
Gross Unrealized Gains	0.4	0.4
Gross Unrealized Losses	(0.8)	(2.6)
Fair Value	128.2	131.5
U.S. Treasury debt securities
Fair Value Disclosure [Line Items]
Amortized Cost	33.8	35.0
Gross Unrealized Gains	0.0	0.1
Gross Unrealized Losses	(0.1)	(0.6)
Fair Value	33.7	34.5
Corporate/Other debt securities
Fair Value Disclosure [Line Items]
Amortized Cost	94.8	98.7
Gross Unrealized Gains	0.4	0.3
Gross Unrealized Losses	(0.7)	(2.0)
Fair Value	$ 94.5	$ 97.0

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Fair Value Disclosure [Line Items]

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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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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