Regulatory Capital and Other Regulatory Matters (Common Share Repurchases) (Details)			3 Months Ended						6 Months Ended		12 Months Ended	84 Months Ended
		Jul. 17, 2023 $ / shares	Jun. 30, 2023 USD ($) $ / shares shares	Mar. 31, 2023 USD ($) $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares	Sep. 30, 2022 USD ($) $ / shares shares	Jun. 30, 2022 USD ($) $ / shares shares	Mar. 31, 2022 USD ($) $ / shares shares	Jun. 30, 2023 $ / shares shares	Jun. 30, 2022 $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares	Jun. 30, 2023 $ / shares shares	Jul. 31, 2023	Feb. 28, 2023 USD ($)	Aug. 31, 2022	Jan. 10, 2022 USD ($)	Dec. 31, 2021 $ / shares shares	Jun. 30, 2016 shares
Accelerated Share Repurchases [Line Items]
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					$ 0.25
Stock repurchased during period, value			$ 2,000,000	$ 27,000,000	$ 51,000,000	$ 415,000,000	$ 600,000,000	$ 584,000,000
Common stock, share reduction												38.00%
Common stock, shares outstanding (in shares) | shares			301,618,768	300,821,000	299,324,357	300,335,000	312,781,000	327,306,000	301,618,768	312,781,000	299,324,357	301,618,768					337,941,000	484,000,000
Minimum capital conservation buffer			0.025						0.025			0.025
Stock repurchased during period, number of shares (in share) | shares			58,000	836,000	1,731,000	12,468,000	15,031,000	12,548,000
Cash dividends declared per common share (in dollars per share) | $ / shares	[1]		$ 0.30				$ 0.30		$ 0.60	$ 0.60
Ally Financial Inc
Accelerated Share Repurchases [Line Items]
Minimum capital conservation buffer			0.025		0.025				0.025		0.025	0.025			0.025
Unsecured debt
Accelerated Share Repurchases [Line Items]
Proceeds from issuance of subordinated long-term debt														$ 500,000,000
Subsequent event
Accelerated Share Repurchases [Line Items]
Cash dividends declared per common share (in dollars per share) | $ / shares		$ 0.30
Subsequent event | Ally Financial Inc
Accelerated Share Repurchases [Line Items]
Minimum capital conservation buffer													0.025
Common stock
Accelerated Share Repurchases [Line Items]
Stock repurchase program, authorized amount																$ 2,000,000,000
Stock repurchased during period, value											$ 1,650,000,000

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