Fair Value Measurements (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 5.0	$ 0.0	$ 6.0
Assets, Fair Value Disclosure [Abstract]
Available for sale securities	5.0
Par value	19.0
Fair Value, Measurements, Recurring
Assets, Fair Value Disclosure [Abstract]
Available for sale securities	5.0	0.0
Trading securities	4.0	5.0
Fair Value, Measurements, Recurring \| Fair Value, Inputs, Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Available for sale securities	0.0	0.0
Trading securities	4.0	5.0
Fair Value, Measurements, Recurring \| Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Available for sale securities	0.0	0.0
Trading securities	0.0	0.0
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3)
Assets, Fair Value Disclosure [Abstract]
Available for sale securities	5.0	0.0
Trading securities	$ 0.0	$ 0.0

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- Definition

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

+ References

No definition available.

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- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with interest rate reset through auction process, sold at par value.

+ References

No definition available.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.4)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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