Regulatory Capital and Other Regulatory Matters - Schedule of Common Share Repurchases (Details) $ / shares in Units, $ in Millions			1 Months Ended				3 Months Ended								12 Months Ended			102 Months Ended
		Jan. 16, 2025 $ / shares	Dec. 31, 2024 USD ($) $ / shares shares	Nov. 30, 2024 USD ($)	Jun. 30, 2024 USD ($) $ / shares shares	Feb. 28, 2023 USD ($)	Dec. 31, 2024 USD ($) $ / shares shares	Sep. 30, 2024 USD ($) $ / shares shares	Jun. 30, 2024 USD ($) $ / shares shares	Mar. 31, 2024 USD ($) $ / shares shares	Dec. 31, 2023 USD ($) $ / shares shares	Sep. 30, 2023 USD ($) $ / shares shares	Jun. 30, 2023 USD ($) $ / shares shares	Mar. 31, 2023 USD ($) $ / shares shares	Dec. 31, 2024 USD ($) $ / shares shares	Dec. 31, 2023 USD ($) $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares	Dec. 31, 2024 $ / shares shares	Oct. 31, 2024	Oct. 31, 2023	Oct. 31, 2022	Jun. 30, 2016 shares
Accelerated Share Repurchases [Line Items]
Minimum capital conservation buffer			0.025				0.025								0.025			0.025
Proceeds from issuance of long-term debt															$ 4,337	$ 5,705	$ 7,125
Stock repurchased during period, value							$ 7	$ 1	$ 1	$ 29	$ 4	$ 0	$ 2	$ 27
Stock repurchased during period, number of shares (in share) | shares							167,000	27,000	13,000	781,000	145,000	5,000	58,000	836,000
Common stock, shares outstanding (in shares) | shares			305,387,550		304,656,000		305,387,550	304,715,000	304,656,000	303,978,000	302,459,258	301,630,000	301,619,000	300,821,000	305,387,550	302,459,258	299,324,000	305,387,550				484,000,000
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	$ 0.30	$ 0.30	$ 0.30		$ 0.30
Common stock, share reduction																		37.00%
Cash dividends declared per common share (in dollars per share) | $ / shares	[1]														$ 1.20	$ 1.20	$ 1.20
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				$ 440	$ 330
Automotive | Credit-Linked Notes | Consumer
Accelerated Share Repurchases [Line Items]
Debt instrument, reference portfolio amount				$ 4,000	$ 3,000				$ 3,000
Ally Financial Inc
Accelerated Share Repurchases [Line Items]
Minimum capital conservation buffer			0.026				0.026				0.025				0.026	0.025		0.026	0.026	0.025	0.025
Unsecured debt
Accelerated Share Repurchases [Line Items]
Proceeds from issuance of long-term debt			$ 500			$ 500

[1] Figures in the table may not recalculate exactly due to rounding. Earnings per share is calculated based on unrounded numbers.