Securitizations and Variable Interest Entities - Schedule of Variable Interest Entities (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Variable Interest Entity [Line Items]
Carrying value of total assets	$ 192,981	$ 196,392	$ 195,704
Carrying value of total liabilities	178,256	182,626
Assets sold to nonconsolidated VIEs	3,149	2,639
Maximum exposure to loss in nonconsolidated VIEs	6,597	5,458
Non-recourse debt	16,807	17,570
Held-to-maturity securities	4,441	4,680
Other assets	9,907	9,395
Equity securities	877	810
On‑balance sheet variable interest entities
Variable Interest Entity [Line Items]
Carrying value of total assets	5,458	7,075
Carrying value of total liabilities	1,720	1,513
Non-recourse debt	1,717	1,509
Other assets	326	461
On‑balance sheet variable interest entities | Consumer | Automotive
Variable Interest Entity [Line Items]
Carrying value of total assets	13,966	16,415
Carrying value of total liabilities	1,829	1,614
Assets sold to nonconsolidated VIEs	0	0
Maximum exposure to loss in nonconsolidated VIEs	0	0
Assets held-in-trust	8,500	9,300
On‑balance sheet variable interest entities | Consumer | Automotive | Nonrecourse
Variable Interest Entity [Line Items]
Non-recourse debt	109	100
Off-balance sheet variable interest entities
Variable Interest Entity [Line Items]
Carrying value of total assets	16,750	19,012
Carrying value of total liabilities	2,811	2,588
Off-balance sheet variable interest entities | Consumer | Automotive
Variable Interest Entity [Line Items]
Carrying value of total assets	103	81
Carrying value of total liabilities	0	0
Assets sold to nonconsolidated VIEs	3,056	2,514
Maximum exposure to loss in nonconsolidated VIEs	3,159	2,595
Held-to-maturity securities	99	78
Other assets	4	3
Off-balance sheet variable interest entities | Consumer | Other
Variable Interest Entity [Line Items]
Carrying value of total assets	0	0
Carrying value of total liabilities	0	0
Assets sold to nonconsolidated VIEs	93	125
Maximum exposure to loss in nonconsolidated VIEs	93	125
Off-balance sheet variable interest entities | Commercial | Other
Variable Interest Entity [Line Items]
Carrying value of total assets	2,681	2,516
Carrying value of total liabilities	982	974
Assets sold to nonconsolidated VIEs	0	0
Maximum exposure to loss in nonconsolidated VIEs	3,345	2,738
Equity securities	$ 48	$ 44