Securitizations and Variable Interest Entities - Schedule of Variable Interest Entities (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024
Variable Interest Entity [Line Items]
Carrying value of total assets	$ 193,331	$ 191,836	$ 192,800
Carrying value of total liabilities	179,099	177,933
Assets sold to nonconsolidated VIEs	2,867	2,971
Maximum exposure to loss in nonconsolidated VIEs	6,462	6,545
Non-recourse debt	16,465	17,495
Held-to-maturity securities	4,668	4,346
Other assets	11,545	10,660
Equity securities	942	871
On‑balance sheet variable interest entities
Variable Interest Entity [Line Items]
Carrying value of total assets	3,994	4,666
Carrying value of total liabilities	1,363	1,565
Non-recourse debt	1,360	1,561
Other assets	311	333
On‑balance sheet variable interest entities | Consumer | Automotive
Variable Interest Entity [Line Items]
Carrying value of total assets	12,043	12,821
Carrying value of total liabilities	1,485	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	122	118
Off-balance sheet variable interest entities
Variable Interest Entity [Line Items]
Carrying value of total assets	14,953	15,681
Carrying value of total liabilities	2,508	2,705
Off-balance sheet variable interest entities | Consumer | Automotive
Variable Interest Entity [Line Items]
Carrying value of total assets	81	92
Carrying value of total liabilities	0	0
Assets sold to nonconsolidated VIEs	2,790	2,885
Maximum exposure to loss in nonconsolidated VIEs	2,871	2,977
Held-to-maturity securities	77	88
Other assets	4	4
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	77	86
Maximum exposure to loss in nonconsolidated VIEs	77	86
Off-balance sheet variable interest entities | Commercial | Other
Variable Interest Entity [Line Items]
Carrying value of total assets	2,829	2,768
Carrying value of total liabilities	1,023	1,022
Assets sold to nonconsolidated VIEs	0	0
Maximum exposure to loss in nonconsolidated VIEs	3,514	3,482
Equity securities	$ 49	$ 50