Marketable Securities (Proceeds from Sale) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Proceeds from maturities and sales	$ 204.5	$ 798.6	$ 1,016.9	$ 1,626.3
Realized gains	0.0	0.0	0.0	0.0
Realized losses	$ 0.0	$ 0.0	$ 0.0	$ 0.0

Proceeds from Sale and Maturity of Debt Securities, Available-for-sale And Cash Equivalents

No definition available.

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- Definition

Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27357-111563

+ Details

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- Definition

Amount of realized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

+ Details

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- References

No definition available.

+ Details

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