Investments in Affiliated Companies (Summarized Financial Data-RRPF) (Details 6) $ in Millions		12 Months Ended
		Dec. 31, 2021 USD ($) AircraftEngines	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Schedule of Equity Method Investments [Line Items]
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment		$ 3,378.8	$ 3,313.3
Income Statement [Abstract]
Depreciation expense		(378.4)	(342.8)	$ (332.7)
Interest expense, net		(204.0)	(190.3)	(180.5)
Income Taxes		(53.2)	(37.3)	(40.9)
Net Income		143.1	151.3	211.2
Assets [Abstract]
Total Assets		9,541.7	8,937.6	7,994.0
EquityMethodInvestmentSummarizedFinancialInformationAPandAccruedExpense		215.8	147.3
Liabilities and Equity [Abstract]
Other liabilities		112.4	135.6
Total Liabilities and Shareholders’ Equity		9,541.7	8,937.6
Total Revenues		1,257.4	1,209.2	1,202.1
Foreign Tax Authority | United Kingdom tax authority
Liabilities and Equity [Abstract]
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount		39.7	12.3
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Income Statement [Abstract]
Gains on sales of assets		79.5	115.7	86.4
Net Income		5.0	146.1	161.4
Assets [Abstract]
Total Assets		4,963.7	5,119.6
Liabilities and Equity [Abstract]
Current liabilities		492.6	311.0
Liabilities, Noncurrent		3,329.6	3,674.7
Total Liabilities and Shareholders’ Equity		4,963.7	5,119.6
Total Revenues		407.4	491.0	469.8
Current assets		574.3	352.7
RRPF Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment		$ 1,415.5	1,283.6
Liabilities and Equity [Abstract]
GATX ownership percentage in joint venture		50.00%
Number of Aircraft Engines Under Leasing Arrangement | AircraftEngines		199
Number of Aircraft Engines Sold | AircraftEngines		21
RRPF Joint Ventures [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Income Statement [Abstract]
Depreciation expense		$ (238.3)	(248.7)	(223.9)
Interest expense, net		(96.7)	(116.0)	(126.4)
Other expenses		(38.5)	(50.3)	(16.5)
Gains on sales of assets		79.5	115.7	86.4
Income Taxes		(107.4)	(45.6)	(27.9)
Net Income		6.0	146.1	161.7
Assets [Abstract]
Total Assets		4,962.9	5,119.6
EquityMethodInvestmentSummarizedFinancialInformationAPandAccruedExpense		130.9	110.4
Liabilities and Equity [Abstract]
Current liabilities		361.8	200.6
Liabilities, Noncurrent		2,845.1	3,243.6
Other liabilities		484.4	431.1
Shareholders’ equity		1,140.7	1,133.9
Total Liabilities and Shareholders’ Equity		4,962.9	5,119.6
Net Assets	[1]	4,389.4	4,766.9
Current assets		573.5	352.7
Income (Loss) Attributable to Parent, before Tax		113.4	191.7	189.6
RRPF Joint Ventures [Member] | Third Parties [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Liabilities and Equity [Abstract]
Total Revenues		195.5	257.6	213.3
RRPF Joint Ventures [Member] | Rolls Royce [Member] | Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Liabilities and Equity [Abstract]
Total Revenues		$ 211.9	$ 233.4	$ 256.7

[1] (a) All operating assets were pledged as collateral for long-term debt obligations.