v3.26.1
Financial Data of Business Segments (Details)
 3 Months Ended
Mar. 31, 2026
USD ($)
Segment
Mar. 31, 2025
USD ($)
Dec. 31, 2025
USD ($)
Segment Reporting [Abstract]      
Number of business segments | Segment 3    
Number of Reportable Segments | Segment 3    
Payment for management fee $ 1,500,000 $ 1,400,000  
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]      
Lease revenue 518,700,000 359,600,000  
Non-dedicated engine revenue 22,100,000 21,500,000  
Other revenue 42,900,000 40,500,000  
Total Revenues 583,700,000 421,600,000  
Maintenance expense 140,700,000 103,500,000  
Depreciation expense 169,200,000 103,600,000  
Operating lease expense 7,400,000 7,600,000  
Other operating expense 21,800,000 16,000,000.0  
Total Expenses 339,100,000 230,700,000  
Net gain on asset dispositions 51,000,000.0 33,400,000  
Interest (expense) income, net (151,000,000.0) (94,900,000)  
Other (expense) income 6,200,000 (2,700,000)  
Share of affiliates' earnings (pre-tax) 27,600,000 33,400,000  
Segment profit (loss) 178,400,000 160,100,000  
Selling, general and administrative expense 71,300,000 56,600,000  
Net Income Attributable to GATX 85,500,000 78,600,000  
Net gains on disposition of owned assets 44,100,000 31,100,000  
Residual sharing income 100,000 100,000  
Non-remarketing net gains 8,500,000 5,800,000  
Asset impairments 1,700,000 3,600,000  
Net gain on asset dispositions 51,000,000.0 33,400,000  
Cash paid for the acquisition of operating assets 4,520,000,000 296,300,000  
Investments in affiliated companies 752,400,000   $ 732,300,000
Identifiable assets 17,944,200,000   17,999,500,000
Income taxes, affiliates' earnings 6,800,000 8,300,000  
Total expenses (1) 410,400,000 287,300,000  
Income taxes expense (benefit) including affiliate's earnings 28,000,000.0 24,900,000  
Net Income 79,100,000 78,600,000  
Net loss (6,400,000) 0  
Brookfield      
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]      
Other revenue 2,800,000    
GABX      
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]      
Depreciation expense  
Rail North America      
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]      
Lease revenue 400,700,000 260,000,000.0  
Other revenue 36,000,000.0 33,300,000  
Total Revenues 436,700,000 293,300,000  
Maintenance expense 120,600,000 83,700,000  
Depreciation expense 126,700,000 70,400,000  
Operating lease expense 7,400,000 7,600,000  
Other operating expense 13,100,000 7,500,000  
Total Expenses 267,800,000 169,200,000  
Net gain on asset dispositions 49,800,000 32,100,000  
Interest (expense) income, net (114,000,000.0) (64,700,000)  
Other (expense) income (800,000) (2,700,000)  
Share of affiliates' earnings (pre-tax) 0 0  
Segment profit (loss) 103,900,000 88,800,000  
Net gains on disposition of owned assets 44,000,000.0 30,500,000  
Residual sharing income 100,000 100,000  
Non-remarketing net gains 7,400,000 5,100,000  
Asset impairments 1,700,000 3,600,000  
Net gain on asset dispositions 49,800,000 32,100,000  
Cash paid for the acquisition of operating assets 4,464,200,000 227,700,000  
Identifiable assets 12,270,100,000   12,235,500,000
Rail North America | RailPulse      
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]      
Investments in affiliated companies 0   0
Rail International      
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]      
Lease revenue 100,400,000 83,600,000  
Other revenue 4,800,000 4,900,000  
Total Revenues 105,200,000 88,500,000  
Maintenance expense 19,100,000 18,500,000  
Depreciation expense 27,800,000 20,100,000  
Operating lease expense 0 0  
Other operating expense 5,300,000 4,600,000  
Total Expenses 52,200,000 43,200,000  
Net gain on asset dispositions 1,100,000 1,300,000  
Interest (expense) income, net (25,000,000.0) (19,100,000)  
Other (expense) income 2,500,000 (1,800,000)  
Share of affiliates' earnings (pre-tax) 0 0  
Segment profit (loss) 31,600,000 25,700,000  
Net gains on disposition of owned assets 0 600,000  
Residual sharing income 0 0  
Non-remarketing net gains 1,100,000 700,000  
Asset impairments 0 0  
Net gain on asset dispositions 1,100,000 1,300,000  
Cash paid for the acquisition of operating assets 47,400,000 62,700,000  
Investments in affiliated companies     0
Identifiable assets 2,812,600,000   2,919,000,000
Rail International | RailPulse      
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]      
Investments in affiliated companies 0    
Engine Leasing      
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]      
Lease revenue 9,500,000 8,100,000  
Non-dedicated engine revenue 22,100,000 21,500,000  
Other revenue 0 0  
Total Revenues 31,600,000 29,600,000  
Other operating expense 3,100,000 2,800,000  
Net gain on asset dispositions 0 0  
Net gains on disposition of owned assets 0 0  
Residual sharing income 0 0  
Non-remarketing net gains 0 0  
Asset impairments 0 0  
Net gain on asset dispositions 0 0  
Cash paid for the acquisition of operating assets 200,000 0  
Investments in affiliated companies     732,300,000
Identifiable assets 1,836,600,000   1,831,600,000
Engine Leasing | RailPulse      
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]      
Investments in affiliated companies 752,400,000    
Other      
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]      
Lease revenue 8,100,000 7,900,000  
Other revenue 2,100,000 2,300,000  
Total Revenues 10,200,000 10,200,000  
Maintenance expense 1,000,000.0 1,300,000  
Depreciation expense 4,100,000 3,700,000  
Operating lease expense 0 0  
Other operating expense 300,000 1,100,000  
Total Expenses 5,400,000 6,100,000  
Net gain on asset dispositions 100,000 0  
Interest (expense) income, net 1,300,000 1,100,000  
Other (expense) income 1,400,000 1,800,000  
Share of affiliates' earnings (pre-tax) 0 0  
Segment profit (loss) 7,600,000 7,000,000.0  
Net gains on disposition of owned assets 100,000 0  
Residual sharing income 0 0  
Non-remarketing net gains 0 0  
Asset impairments 0 0  
Net gain on asset dispositions 100,000 0  
Cash paid for the acquisition of operating assets 8,200,000 5,900,000  
Investments in affiliated companies     0
Identifiable assets 1,024,900,000   $ 1,013,400,000
Other | RailPulse      
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]      
Investments in affiliated companies 0    
Portfolio Management      
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]      
Maintenance expense 0 0  
Depreciation expense 10,600,000 9,400,000  
Operating lease expense 0 0  
Total Expenses 13,700,000 12,200,000  
Net gain on asset dispositions 0 0  
Interest (expense) income, net (13,300,000) (12,200,000)  
Other (expense) income 3,100,000 0  
Share of affiliates' earnings (pre-tax) 27,600,000 33,400,000  
Segment profit (loss) 35,300,000 38,600,000  
Net gain on asset dispositions $ 0 $ 0