Income Taxes (Details 3) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Summary of reasons for difference between GATX's effective income tax rate and federal statutory income tax
Income taxes at federal statutory rate	$ 94.6	$ 80.9	$ 55.6
Adjust for effect of:
GATX income taxes on sale of AAE	0.0	0.0	23.2
Foreign tax credits	0.0	0.0	(3.9)
Foreign earnings taxed at lower rates	(6.2)	(8.5)	(10.3)
Tax effect of foreign dividends	0.9	0.0	0.0
Corporate owned life insurance	(0.9)	(0.6)	(0.5)
State income taxes	7.6	4.1	1.5
State deferred tax rate change impact	14.1	0.0	0.0
Other	0.8	(0.2)	(0.1)
Income taxes	$ 110.9	$ 75.7	$ 65.5
Effective income tax rate	41.00%	32.70%	41.20%