Regulatory Capital and Other Regulatory Matters - Schedule of Common Share Repurchases (Details) |
1 Months Ended | 3 Months Ended | 12 Months Ended | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
Apr. 14, 2026
$ / shares
|
Dec. 31, 2024
USD ($)
shares
|
Mar. 31, 2026
USD ($)
$ / shares
shares
|
Dec. 31, 2025
USD ($)
$ / shares
shares
|
Sep. 30, 2025
USD ($)
$ / shares
shares
|
Jun. 30, 2025
USD ($)
$ / shares
shares
|
Mar. 31, 2025
USD ($)
$ / shares
shares
|
Dec. 31, 2025
USD ($)
$ / shares
shares
|
Dec. 31, 2024
USD ($)
shares
|
Oct. 31, 2025 |
Oct. 31, 2024 |
|||
| Accelerated Share Repurchases [Line Items] | |||||||||||||
| Minimum capital conservation buffer | 0.025 | ||||||||||||
| Proceeds from issuance of long-term debt | $ 1,081,000,000 | $ 24,000,000 | |||||||||||
| Stock repurchase program, authorized | $ 2,000,000,000.0 | $ 2,000,000,000.0 | |||||||||||
| Stock repurchased during period, value | $ 147,000,000 | $ 23,000,000 | $ 1,000,000 | $ 1,000,000 | $ 34,000,000 | ||||||||
| Stock repurchased during period, number of shares (in share) | shares | 3,624,000 | 543,000 | 25,000 | 27,000 | 877,000 | ||||||||
| Common stock, shares outstanding (in shares) | shares | 305,388,000 | 307,407,671 | 308,492,929 | 307,828,000 | 307,787,000 | 307,152,000 | 308,492,929 | 305,388,000 | |||||
| Dividends declared (in dollars per share) | $ / shares | $ 0.30 | $ 0.30 | $ 0.30 | $ 0.30 | $ 0.30 | $ 0.30 | |||||||
| Cash dividends declared per common share (in dollars per share) | $ / shares | [1] | $ 0.30 | $ 0.30 | ||||||||||
| Subsequent event | |||||||||||||
| Accelerated Share Repurchases [Line Items] | |||||||||||||
| Cash dividends declared per common share (in dollars per share) | $ / shares | $ 0.30 | ||||||||||||
| Credit-Linked Notes | |||||||||||||
| Accelerated Share Repurchases [Line Items] | |||||||||||||
| Proceeds from issuance of long-term debt | $ 1,100,000,000 | $ 770,000,000 | |||||||||||
| Consumer automotive | Credit-Linked Notes | Consumer | |||||||||||||
| Accelerated Share Repurchases [Line Items] | |||||||||||||
| Debt instrument, reference portfolio amount | $ 7,000,000,000.0 | $ 10,000,000,000.0 | 10,000,000,000.0 | $ 7,000,000,000.0 | |||||||||
| Debt instrument, reference asset amount | $ 10,700,000,000 | $ 12,100,000,000 | $ 12,100,000,000 | ||||||||||
| Ally Financial Inc | |||||||||||||
| Accelerated Share Repurchases [Line Items] | |||||||||||||
| Minimum capital conservation buffer | 0.026 | 0.026 | 0.026 | 0.026 | 0.026 | ||||||||
| Unsecured | |||||||||||||
| Accelerated Share Repurchases [Line Items] | |||||||||||||
| Proceeds from issuance of long-term debt | $ 500,000,000 | ||||||||||||
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