Legal Proceedings Legal Proceedings (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2021
Legal Proceedings [Line Items]
Deferred Prosecution Agreement Liability - Total Obligation		$ 2,510.0
Controlling Interest Ownership Percentage After Acquisition	80.00%
Payments to Acquire Interest in Joint Venture	$ 4,200.0
Criminal Monetary Penalty
Legal Proceedings [Line Items]
Deferred Prosecution Agreement Liability		243.6
Beneficiary Compensation
Legal Proceedings [Line Items]
Deferred Prosecution Agreement Liability		500.0
Total Criminal Monetary Penalty and Beneficiary Compensation
Legal Proceedings [Line Items]
Deferred Prosecution Agreement Liability		743.6
737 MAX Customer Concessions & Other Considerations Liability
Legal Proceedings [Line Items]
Deferred Prosecution Agreement Liability		$ 1,770.0