Leases Lessee, Schedule of Finance Leases (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) tankContainer	Dec. 31, 2020 USD ($) tankContainer	Dec. 31, 2019 USD ($) tankContainer
Lessee, Lease, Description [Line Items]
Finance Lease, Right-of-Use Asset	$ 1.5	$ 37.5
Capital Leases, Lessee Balance Sheet, Assets by Major Class, Accumulated Depreciation	0.0	(0.3)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	$ 195.1	$ 125.3	$ 145.2
Number of railcars received | tankContainer	2,329	732	157
gatxOperatingLeaseOtherIncome	$ 74.8	$ 88.9	$ 88.2
Railcars [Member]
Lessee, Lease, Description [Line Items]
Finance Lease, Right-of-Use Asset, before Accumulated Amortization	$ 1.5	$ 37.8