Securitizations and Variable Interest Entities - Schedule of Variable Interest Entities (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024	Sep. 30, 2024
Variable Interest Entity [Line Items]
Carrying value of total assets	$ 191,711	$ 191,836	$ 192,670
Carrying value of total liabilities	176,594	177,933
Assets sold to nonconsolidated VIEs	3,057	2,971
Maximum exposure to loss in nonconsolidated VIEs	6,696	6,545
Non-recourse debt	16,749	17,495
Held-to-maturity securities	4,433	4,346
Other assets	10,695	10,660
Equity securities	865	871
Variable Interest Entity
Variable Interest Entity [Line Items]
Carrying value of total assets	14,406	15,681
Carrying value of total liabilities	1,911	2,705
On‑balance sheet variable interest entities
Variable Interest Entity [Line Items]
Carrying value of total assets	2,812	4,666
Carrying value of total liabilities	914	1,565
Non-recourse debt	912	1,561
Other assets	248	333
On‑balance sheet variable interest entities | Consumer | Automotive
Variable Interest Entity [Line Items]
Carrying value of total assets	11,560	12,821
Carrying value of total liabilities	1,054	1,683
Assets sold to nonconsolidated VIEs	0	0
Maximum exposure to loss in nonconsolidated VIEs	0	0
Assets held-in-trust	8,700	8,200
On‑balance sheet variable interest entities | Consumer | Automotive | Nonrecourse
Variable Interest Entity [Line Items]
Non-recourse debt	140	118
Off-balance sheet variable interest entities | Consumer | Automotive
Variable Interest Entity [Line Items]
Carrying value of total assets	61	92
Carrying value of total liabilities	0	0
Assets sold to nonconsolidated VIEs	3,057	2,885
Maximum exposure to loss in nonconsolidated VIEs	3,118	2,977
Held-to-maturity securities	58	88
Other assets	3	4
Off-balance sheet variable interest entities | Consumer | Other
Variable Interest Entity [Line Items]
Carrying value of total assets		0
Carrying value of total liabilities		0
Assets sold to nonconsolidated VIEs		86
Maximum exposure to loss in nonconsolidated VIEs		86
Off-balance sheet variable interest entities | Commercial | Other
Variable Interest Entity [Line Items]
Carrying value of total assets	2,785	2,768
Carrying value of total liabilities	857	1,022
Assets sold to nonconsolidated VIEs	0	0
Maximum exposure to loss in nonconsolidated VIEs	3,578	3,482
Equity securities	$ 54	$ 50