Fair Value Measurements (Changes in Level 3 Assets) (Details) - Auction Rate - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value assets beginning balance	$ 2.8	$ 4.1	$ 4.3	$ 4.7
Total Gains (Losses):
Included in Earnings			0.0	0.0
Included in Other Comprehensive Income	0.1	0.0	0.1	0.0
Purchases, Issues, Sales, and Settlements
Sales	0.0	0.0	0.0	0.0
Settlements	0.0	0.0	(1.5)	(0.6)
Fair value assets ending balance	$ 2.9	$ 4.1	$ 2.9	$ 4.1

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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-Section 50
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- Definition

Amount of gain (loss) recognized in other comprehensive income (loss) for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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- References

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Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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