Summary of Significant Accounting Policies Aircraft Maintenance and Repair Costs (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
A320 Series Engine
Servicing Asset at Amortized Cost [Line Items]
Deferred Costs for Heavy Maintenance	$ 12.8	$ 64.1
Amortization of Other Deferred Charges	17.6	11.1
Airbus A320 Aircraft Series
Servicing Asset at Amortized Cost [Line Items]
Deferred Costs for Heavy Maintenance	22.6	18.4
Amortization of Other Deferred Charges	$ 19.9	$ 14.9

Amount of amortization of other deferred costs recognized in the income statement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.3)
-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration