Regulatory Capital and Other Regulatory Matters (Schedule of Regulatory Capital Amount and Ratios) (Details) $ in Millions	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
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	$ 4,000
Percentage of interest-bearing domestic deposits to deposits, brokered	2.80%
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	0.0997	0.1034
Minimum capital conservation buffer	0.035	0.035
Common equity tier one capital	$ 14,849	$ 15,143
Tier one capital to risk-weighted assets, amount	$ 17,124	$ 17,403
Tier one capital to risk-weighted assets, ratio	0.1149	0.1189
Tier one capital to risk-weighted assets, well-capitalized minimum	0.0600
Capital to risk-weighted assets, amount	$ 19,564	$ 19,724
Capital to risk-weighted assets, ratio	0.1313	0.1347
Capital to risk weighted assets, well-capitalzed minimum	0.1000
Tier one leverage to adjusted quarterly average assets, amount	$ 17,124	$ 17,403
Tier one leverage to adjusted quarterly average assets, ratio	0.0936	0.0967
Ally Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity tier one capital ratio	0.1209	0.1239
Minimum capital conservation buffer	0.025	0.025
Common equity tier one capital	$ 17,220	$ 17,253
Common equity tier one capital, well capitalized minimum	0.0650
Tier one capital to risk-weighted assets, amount	$ 17,220	$ 17,253
Tier one capital to risk-weighted assets, ratio	0.1209	0.1239
Tier one capital to risk-weighted assets, well-capitalized minimum	0.0800
Capital to risk-weighted assets, amount	$ 19,006	$ 18,995
Capital to risk-weighted assets, ratio	0.1334	0.1364
Capital to risk weighted assets, well-capitalzed minimum	0.1000
Tier one leverage to adjusted quarterly average assets, amount	$ 17,220	$ 17,253
Tier one leverage to adjusted quarterly average assets, ratio	0.0993	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