3. Fair Value Measurements Available-for-Sale Investments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	$ 267.6
Debt Securities, Available-for-sale, Amortized Cost	262.2
Fair Value, Recurring [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	267.6	$ 402.9
Fair Value, Recurring [Member] \| Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	133.2	204.5
Fair Value, Recurring [Member] \| Municipal Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	15.2	11.6
Fair Value, Recurring [Member] \| Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	36.2	72.9
Fair Value, Recurring [Member] \| US Government Sponsored Agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	76.9	106.1
Fair Value, Recurring [Member] \| Foreign Government Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	4.0	4.7
Fair Value, Recurring [Member] \| Foreign Government Debt [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	2.1	3.1
Fair Value, Recurring [Member] \| Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	267.6	402.9
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.0	(0.4)
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	5.4	2.4
Debt Securities, Available-for-sale, Allowance for Credit Loss	0.0
Debt Securities, Available-for-sale, Amortized Cost	262.2	400.9
Short-term Investments [Member] \| Fair Value, Recurring [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	267.5	402.8
Short-term Investments [Member] \| Fair Value, Recurring [Member] \| Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	133.2	204.5
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.0	(0.1)
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	2.7	1.4
Debt Securities, Available-for-sale, Allowance for Credit Loss	0.0
Debt Securities, Available-for-sale, Amortized Cost	130.5	203.2
Short-term Investments [Member] \| Fair Value, Recurring [Member] \| Municipal Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	15.2	11.6
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.0	0.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.2	0.1
Debt Securities, Available-for-sale, Allowance for Credit Loss	0.0
Debt Securities, Available-for-sale, Amortized Cost	15.0	11.5
Short-term Investments [Member] \| Fair Value, Recurring [Member] \| Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	36.1	72.8
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.0	(0.1)
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.3	0.2
Debt Securities, Available-for-sale, Allowance for Credit Loss	0.0
Debt Securities, Available-for-sale, Amortized Cost	35.8	72.7
Short-term Investments [Member] \| Fair Value, Recurring [Member] \| US Government Sponsored Agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	76.9	106.1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.0	(0.2)
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	2.2	0.7
Debt Securities, Available-for-sale, Allowance for Credit Loss	0.0
Debt Securities, Available-for-sale, Amortized Cost	74.7	105.6
Short-term Investments [Member] \| Fair Value, Recurring [Member] \| Foreign Government Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	4.0	4.7
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.0	0.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.0	0.0
Debt Securities, Available-for-sale, Allowance for Credit Loss	0.0
Debt Securities, Available-for-sale, Amortized Cost	4.0	4.7
Short-term Investments [Member] \| Fair Value, Recurring [Member] \| Foreign Government Debt [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	2.1	3.1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.0	0.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.0	0.0
Debt Securities, Available-for-sale, Allowance for Credit Loss	0.0
Debt Securities, Available-for-sale, Amortized Cost	2.1	3.1
Short-term Investments [Member] \| Fair Value, Recurring [Member] \| Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	267.5	402.8
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.0	(0.4)
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	5.4	2.4
Debt Securities, Available-for-sale, Allowance for Credit Loss	0.0
Debt Securities, Available-for-sale, Amortized Cost	262.1	400.8
Other Long-term Investments [Member] \| Fair Value, Recurring [Member] \| Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	0.1	0.1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.0	0.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.0	0.0
Debt Securities, Available-for-sale, Allowance for Credit Loss	0.0
Debt Securities, Available-for-sale, Amortized Cost	0.1	0.1
Other Long-term Investments [Member] \| Fair Value, Recurring [Member] \| Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale	0.1	0.1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.0	0.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	0.0	0.0
Debt Securities, Available-for-sale, Allowance for Credit Loss	0.0
Debt Securities, Available-for-sale, Amortized Cost	$ 0.1	$ 0.1

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) 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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amortized cost of 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 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121558606&loc=SL82898722-210454

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of 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 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121558606&loc=SL82898722-210454

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121553693&loc=d3e26610-111562

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesDebtSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of allowance for credit loss 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 326
-SubTopic 30
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121582814&loc=SL82922900-210455

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 9
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=121582814&loc=SL82922900-210455

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aaa)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121558606&loc=SL82898722-210454

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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.

+ Details

Name:	us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MunicipalBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USTreasuryAndGovernmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ForeignGovernmentDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ForeignGovernmentDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_DebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_ShortTermInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherLongTermInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: