Finance Receivables and Loans, Net (Allowance for Credit Losses on Financing Receivables) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Allowance, beginning balance	$ 3,711	$ 3,267
Charge-offs	(2,720)	(1,628)
Recoveries	833	676
Net charge-offs	(1,887)	(952)
Write-downs from transfers to held-for-sale	(215)
Provision for credit losses	1,979	1,396
Other	(1)	0
Allowance, ending balance	3,587	3,711
Disposal Group, Held-for-Sale, Not Discontinued Operations | Ally Lending
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision for credit losses	16
Unfunded lending commitments	5
Unfunded Loan Commitment
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Provision for credit losses	(11)	3
Consumer
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Charge-offs	(2,590)
Consumer | Automotive
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Allowance, beginning balance	3,020	2,769
Charge-offs	(2,284)	(1,434)
Recoveries	793	649
Net charge-offs	(1,491)	(785)
Write-downs from transfers to held-for-sale	(41)
Provision for credit losses	1,595	1,036
Other	0	0
Allowance, ending balance	3,083	3,020
Consumer | Consumer mortgage
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Allowance, beginning balance	27	27
Charge-offs	(3)	(3)
Recoveries	9	12
Net charge-offs	6	9
Write-downs from transfers to held-for-sale	0
Provision for credit losses	(11)	(8)
Other	(1)	(1)
Allowance, ending balance	21	27
Consumer | Consumer other
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Allowance, beginning balance	426	221
Charge-offs	(303)	(133)
Recoveries	25	12
Net charge-offs	(278)	(121)
Write-downs from transfers to held-for-sale	(174)
Provision for credit losses	319	326
Other	0	0
Allowance, ending balance	293	426
Fair value, option, carrying amount, financing receivable, no allowance		3	$ 7
Commercial
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Allowance, beginning balance	238	250
Charge-offs	(130)	(58)
Recoveries	6	3
Net charge-offs	(124)	(55)
Write-downs from transfers to held-for-sale	0
Provision for credit losses	76	42
Other	0	1
Allowance, ending balance	190	$ 238
Commercial | Automotive
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Charge-offs	(24)
Commercial | Consumer other
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Charge-offs	$ (106)