Securitizations and Variable Interest Entities - Schedule of Variable Interest Entities (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024	Jun. 30, 2024
Variable Interest Entity [Line Items]
Carrying value of total assets	$ 189,473	$ 191,836	$ 192,379
Carrying value of total liabilities	174,926	177,933
Assets sold to nonconsolidated VIEs	2,909	2,971
Maximum exposure to loss in nonconsolidated VIEs	6,501	6,545
Non-recourse debt	15,876	17,495
Held-to-maturity securities	4,561	4,346
Other assets	10,102	10,660
Equity securities	938	871
On‑balance sheet variable interest entities
Variable Interest Entity [Line Items]
Carrying value of total assets	3,360	4,666
Carrying value of total liabilities	1,125	1,565
Non-recourse debt	1,123	1,561
Other assets	264	333
On‑balance sheet variable interest entities | Consumer | Automotive
Variable Interest Entity [Line Items]
Carrying value of total assets	11,506	12,821
Carrying value of total liabilities	1,252	1,683
Assets sold to nonconsolidated VIEs	0	0
Maximum exposure to loss in nonconsolidated VIEs	0	0
Assets held-in-trust	8,100	8,200
On‑balance sheet variable interest entities | Consumer | Automotive | Nonrecourse
Variable Interest Entity [Line Items]
Non-recourse debt	127	118
Off-balance sheet variable interest entities
Variable Interest Entity [Line Items]
Carrying value of total assets	14,404	15,681
Carrying value of total liabilities	2,216	2,705
Off-balance sheet variable interest entities | Consumer | Automotive
Variable Interest Entity [Line Items]
Carrying value of total assets	70	92
Carrying value of total liabilities	0	0
Assets sold to nonconsolidated VIEs	2,909	2,885
Maximum exposure to loss in nonconsolidated VIEs	2,979	2,977
Held-to-maturity securities	67	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	2,828	2,768
Carrying value of total liabilities	964	1,022
Assets sold to nonconsolidated VIEs	0	0
Maximum exposure to loss in nonconsolidated VIEs	3,522	3,482
Equity securities	$ 51	$ 50