Regulatory Capital and Other Regulatory Matters (Schedule of Regulatory Capital Amount and Ratios) (Details) $ in Millions	Sep. 30, 2022 USD ($)	Aug. 31, 2022	Dec. 31, 2021 USD ($)	Sep. 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	$ 9,600
Percentage of interest-bearing domestic deposits to deposits, brokered	6.60%
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	0.0930		0.1034
Minimum capital conservation buffer	0.035	0.025	0.035	0.035
Common equity tier one capital	$ 14,441		$ 15,143
Tier one capital to risk-weighted assets, amount	$ 16,716		$ 17,403
Tier one capital to risk-weighted assets, ratio	0.1077		0.1189
Tier one capital to risk-weighted assets, well-capitalized minimum	0.0600
Capital to risk-weighted assets, amount	$ 19,238		$ 19,724
Capital to risk-weighted assets, ratio	0.1239		0.1347
Capital to risk weighted assets, well-capitalized minimum	0.1000
Tier one leverage to adjusted quarterly average assets, amount	$ 16,716		$ 17,403
Tier one leverage to adjusted quarterly average assets, ratio	0.0878		0.0967
Ally Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity tier one capital ratio	0.1175		0.1239
Minimum capital conservation buffer	0.025		0.025
Common equity tier one capital	$ 17,302		$ 17,253
Common equity tier one capital, well capitalized minimum	0.0650
Tier one capital to risk-weighted assets, amount	$ 17,302		$ 17,253
Tier one capital to risk-weighted assets, ratio	0.1175		0.1239
Tier one capital to risk-weighted assets, well-capitalized minimum	0.0800
Capital to risk-weighted assets, amount	$ 19,152		$ 18,995
Capital to risk-weighted assets, ratio	0.1300		0.1364
Capital to risk weighted assets, well-capitalized minimum	0.1000
Tier one leverage to adjusted quarterly average assets, amount	$ 17,302		$ 17,253
Tier one leverage to adjusted quarterly average assets, ratio	0.0962		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