Regulatory Capital and Other Regulatory Matters (Tables)

3 Months Ended

Mar. 31, 2018

Regulatory Capital Requirements [Abstract]

Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table Text Block]

The following table summarizes our capital ratios under the U.S. Basel III capital framework.

	March 31, 2018				December 31, 2017				Required minimum (a)		Well-capitalized minimum
($ in millions)	Amount		Ratio		Amount		Ratio
Capital ratios
Common Equity Tier 1 (to risk-weighted assets)
Ally Financial Inc.	$	13,079	9.26	%	$	13,237	9.53	%	4.50	%	(b)
Ally Bank	16,535		13.93		17,059		15.04		4.50		6.50	%
Tier 1 (to risk-weighted assets)
Ally Financial Inc.	$	15,512	10.98	%	$	15,628	11.25	%	6.00	%	6.00	%
Ally Bank	16,535		13.93		17,059		15.04		6.00		8.00
Total (to risk-weighted assets)
Ally Financial Inc.	$	17,760	12.57	%	$	17,974	12.94	%	8.00	%	10.00	%
Ally Bank	17,480		14.72		17,886		15.77		8.00		10.00
Tier 1 leverage (to adjusted quarterly average assets) (c)
Ally Financial Inc.	$	15,512	9.26	%	$	15,628	9.53	%	4.00	%	(b)
Ally Bank	16,535		11.94		17,059		12.87		4.00		5.00	%

(a) In addition to the minimum risk-based capital requirements for common equity Tier 1 capital, Tier 1 capital, and total capital ratios, Ally and Ally Bank were required to maintain a minimum capital conservation buffer of 1.875% and 1.25% at March 31, 2018, and December 31, 2017, respectively, which ultimately increases to 2.5% on January 1, 2019.

(b) Currently, there is no ratio component for determining whether a BHC is “well-capitalized.”

(c) Federal regulatory reporting guidelines require the calculation of adjusted quarterly average assets using a daily average methodology.

Schedule of Common Share Repurchase Activity [Table Text Block]

The following table presents information related to our common stock for each quarter since the commencement of our common stock repurchase programs and initiation of a quarterly cash dividend on common stock.

	Common stock repurchased during period (a)			Number of common shares outstanding		Cash dividends declared per common share (b)
($ in millions, except per share data; shares in thousands)	Approximate dollar value		Number of shares	Beginning of period	End of period
2016
Third quarter	$	159	8,298	483,753	475,470	$	0.08
Fourth quarter	167		8,745	475,470	467,000	0.08
2017
First quarter	$	169	8,097	467,000	462,193	$	0.08
Second quarter	204		10,485	462,193	452,292	0.08
Third quarter	190		8,507	452,292	443,796	0.12
Fourth quarter	190		7,033	443,796	437,054	0.12
2018
First quarter	$	185	6,473	437,054	432,691	$	0.13

(a) Includes shares of common stock withheld to cover income taxes owed by participants in our share-based incentive plans.

(b) On April 10, 2018, the Board declared a quarterly cash dividend of $0.13 per share on all common stock, payable on May 15, 2018. Refer to Note 25 for further information regarding this common stock dividend.