Fair Value - Schedule of Fair Value Measurements - Nonrecurring Basis (Details) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
	Dec. 31, 2024	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	$ 160	$ 209		$ 160
Finance receivables and loans, net	132,316	130,087		132,316
Goodwill impairment		305	$ 0	118
Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	143	203		143
Lower-of-cost-or-fair-value reserve, valuation reserve, or cumulative adjustments	0	0		0
Goodwill impairment	118
Assets | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	552	311		552
Lower-of-cost-or-fair-value reserve, valuation reserve, or cumulative adjustments	(184)	(85)		(184)
Goodwill | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill	362			362
Lower-of-cost-or-fair-value reserve, valuation reserve, or cumulative adjustments	(118)			(118)
Repossessed and foreclosed assets | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	8	10		8
Lower-of-cost-or-fair-value reserve, valuation reserve, or cumulative adjustments	(1)	(2)		(1)
Level 1 | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	0	0		0
Level 1 | Assets | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0		0
Level 1 | Goodwill | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill	0			0
Level 1 | Repossessed and foreclosed assets | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	0	0		0
Level 2 | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	0	0		0
Level 2 | Assets | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0		0
Level 2 | Goodwill | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill	0			0
Level 2 | Repossessed and foreclosed assets | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	0	0		0
Level 3 | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	143	203		143
Level 3 | Assets | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	552	311		552
Level 3 | Goodwill | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill	362			362
Level 3 | Repossessed and foreclosed assets | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	8	10		8
Commercial | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	39	98		39
Lower-of-cost-or-fair-value reserve, valuation reserve, or cumulative adjustments	(65)	(83)		(65)
Commercial | Level 1 | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	0	0		0
Commercial | Level 2 | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	0	0		0
Commercial | Level 3 | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	39	98		39
Automotive | Commercial | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	13	77		13
Lower-of-cost-or-fair-value reserve, valuation reserve, or cumulative adjustments	(2)	(16)		(2)
Automotive | Commercial | Level 1 | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	0	0		0
Automotive | Commercial | Level 2 | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	0	0		0
Automotive | Commercial | Level 3 | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	13	77		13
Other | Commercial | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	26	21		26
Lower-of-cost-or-fair-value reserve, valuation reserve, or cumulative adjustments	(63)	(67)		(63)
Other | Commercial | Level 1 | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	0	0		0
Other | Commercial | Level 2 | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	0	0		0
Other | Commercial | Level 3 | Nonrecurring fair value measurements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	$ 26	$ 21		$ 26