Regulatory Capital and Other Regulatory Matters - Schedule of Common Share Repurchases (Details) |
1 Months Ended | 3 Months Ended | 6 Months Ended | 12 Months Ended | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
Jul. 17, 2026
$ / shares
|
Dec. 31, 2024
USD ($)
shares
|
Jun. 30, 2026
USD ($)
$ / shares
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
|
Jun. 30, 2026
USD ($)
$ / shares
shares
|
Jun. 30, 2025
USD ($)
$ / shares
shares
|
Dec. 31, 2025
USD ($)
$ / shares
shares
|
Dec. 31, 2024
USD ($)
shares
|
Oct. 31, 2025 |
Oct. 31, 2024 |
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| Accelerated Share Repurchases [Line Items] | ||||||||||||||||
| Minimum capital conservation buffer | 0.025 | 0.025 | ||||||||||||||
| Proceeds from issuance of long-term debt | $ 1,877,000,000 | $ 953,000,000 | ||||||||||||||
| Stock repurchase program, authorized | $ 2,000,000,000.0 | $ 2,000,000,000.0 | ||||||||||||||
| Stock repurchased during period, value | $ 148,000,000 | $ 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 | 3,371,000 | 3,624,000 | 543,000 | 25,000 | 27,000 | 877,000 | ||||||||||
| Common stock, shares outstanding (in shares) | shares | 305,388,000 | 304,542,540 | 307,408,000 | 308,492,929 | 307,828,000 | 307,787,000 | 307,152,000 | 304,542,540 | 307,787,000 | 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 | $ 0.30 | $ 0.30 | $ 0.30 | |||||||
| Cash dividends declared per common share (in dollars per share) | $ / shares | [1] | $ 0.30 | $ 0.30 | $ 0.60 | $ 0.60 | |||||||||||
| Series D Preferred Stock | ||||||||||||||||
| Accelerated Share Repurchases [Line Items] | ||||||||||||||||
| Stock issued during period, value, new issues | $ 987,000,000 | $ 987,000,000 | ||||||||||||||
| 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 | 550,000,000 | $ 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 | 5,000,000,000.0 | $ 10,000,000,000.0 | 5,000,000,000.0 | 10,000,000,000.0 | $ 7,000,000,000.0 | ||||||||||
| Debt instrument, reference asset amount | $ 13,900,000,000 | $ 12,100,000,000 | $ 13,900,000,000 | $ 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 | 0.026 | ||||||||||
| Unsecured | ||||||||||||||||
| Accelerated Share Repurchases [Line Items] | ||||||||||||||||
| Proceeds from issuance of long-term debt | $ 500,000,000 | |||||||||||||||
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