Regulatory Capital and Other Regulatory Matters (Schedule of Regulatory Capital Amount and Ratios) (Details) $ in Millions	Oct. 01, 2022	Jun. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)	Jun. 30, 2021
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
BHC enhanced prudential standards, minimum		$ 100,000
BHC enhanced prudential standards, maximum		250,000
Average wSTWF exemption threshold		$ 50,000
Minimum capital conservation buffer		0.025
Brokered deposits		$ 7,000
Percentage of interest-bearing domestic deposits to deposits, brokered		5.00%
Accounting Standards Update 2016-13
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Phase-in of capital impact of Accounting Standards Update 2016-13		25.00%
CECL scaling factor		25.00%
Deferred reduction to Common Equity Tier 1 Capital from CECL		$ 887
Ally Financial Inc
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity tier one capital ratio		0.0962	0.1034
Minimum capital conservation buffer		0.035	0.035	0.035
Common equity tier one capital		$ 14,650	$ 15,143
Tier one capital to risk-weighted assets, amount		$ 16,925	$ 17,403
Tier one capital to risk-weighted assets, ratio		0.1111	0.1189
Tier one capital to risk-weighted assets, well-capitalized minimum		0.0600
Capital to risk-weighted assets, amount		$ 19,409	$ 19,724
Capital to risk-weighted assets, ratio		0.1275	0.1347
Capital to risk weighted assets, well-capitalzed minimum		0.1000
Tier one leverage to adjusted quarterly average assets, amount		$ 16,925	$ 17,403
Tier one leverage to adjusted quarterly average assets, ratio		0.0910	0.0967
Ally Financial Inc | Forecast
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Minimum capital conservation buffer	0.025
Ally Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity tier one capital ratio		0.1198	0.1239
Minimum capital conservation buffer		0.025	0.025
Common equity tier one capital		$ 17,349	$ 17,253
Common equity tier one capital, well capitalized minimum		0.0650
Tier one capital to risk-weighted assets, amount		$ 17,349	$ 17,253
Tier one capital to risk-weighted assets, ratio		0.1198	0.1239
Tier one capital to risk-weighted assets, well-capitalized minimum		0.0800
Capital to risk-weighted assets, amount		$ 19,166	$ 18,995
Capital to risk-weighted assets, ratio		0.1324	0.1364
Capital to risk weighted assets, well-capitalzed minimum		0.1000
Tier one leverage to adjusted quarterly average assets, amount		$ 17,349	$ 17,253
Tier one leverage to adjusted quarterly average assets, ratio		0.0983	0.1012
Tier one leverage to adjusted quarterly average assets, well-capitalized minimum		0.0500
Minimum
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity tier one capital ratio		0.045
Tier one capital to risk-weighted assets, required minimum		0.06
Capital to risk-weighted assets, required minimum		0.08
Tier one leverage ratio, minimum		0.04
Minimum | Ally Financial Inc
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity tier one capital ratio		0.0450
Tier one capital to risk-weighted assets, required minimum		0.0600
Capital to risk-weighted assets, required minimum		0.0800
Tier one leverage ratio, minimum		0.0400
Minimum | Ally Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity tier one capital ratio		0.0450
Tier one capital to risk-weighted assets, required minimum		0.0600
Capital to risk-weighted assets, required minimum		0.0800
Tier one leverage ratio, minimum		0.0400