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Commitments and Contingencies - Narrative (Details) - USD ($)
 1 Months Ended 3 Months Ended 9 Months Ended
Sep. 30, 2025
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Dec. 31, 2024
May 04, 2023
Loss Contingencies [Line Items]              
IDA balance floor amount             $ 60,000,000,000
IDA balance ceiling amount             $ 90,000,000,000
Additions (reductions) in deposit balance $ 3,000,000,000            
Ending IDA balance 78,600,000,000 $ 78,600,000,000   $ 78,600,000,000   $ 87,600,000,000  
Fixed-rate obligation IDA balance 59,700,000,000 59,700,000,000   59,700,000,000   66,600,000,000  
Floating-rate obligation IDA balance 18,900,000,000 18,900,000,000   18,900,000,000   $ 21,000,000,000.0  
Guarantees              
Loss Contingencies [Line Items]              
Liability for guarantees $ 0 0   0      
Residential real estate | First Mortgages              
Loss Contingencies [Line Items]              
Purchased during period   1,700,000,000 $ 1,100,000,000 4,400,000,000 $ 2,600,000,000    
Residential real estate | HELOCs              
Loss Contingencies [Line Items]              
Purchased during period   $ 52,000,000 $ 38,000,000 $ 181,000,000 $ 121,000,000