Fair Value - Schedule of Fair Value Measurements - Nonrecurring Basis (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended		12 Months Ended
	Dec. 31, 2024	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	$ 160	$ 185		$ 185		$ 160
Finance receivables and loans, net	132,316	129,813		129,813		132,316
Goodwill impairment		0	$ 0	305	$ 0	118
Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	143	185		185		143
Lower-of-cost-or-fair-value reserve, valuation reserve, or cumulative adjustments	0	(2)		(2)		0
Goodwill impairment	118
Assets | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	552	243		243		552
Lower-of-cost-or-fair-value reserve, valuation reserve, or cumulative adjustments	(184)	(86)		(86)		(184)
Goodwill | Fair Value, Nonrecurring
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)
Nonmarketable equity investments | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets		0		0
Lower-of-cost-or-fair-value reserve, valuation reserve, or cumulative adjustments		(5)		(5)
Repossessed and foreclosed assets | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	8	8		8		8
Lower-of-cost-or-fair-value reserve, valuation reserve, or cumulative adjustments	(1)	(2)		(2)		(1)
Level 1 | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	0	0		0		0
Level 1 | Assets | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0		0		0
Level 1 | Goodwill | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill	0					0
Level 1 | Nonmarketable equity investments | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets		0		0
Level 1 | Repossessed and foreclosed assets | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	0	0		0		0
Level 2 | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	0	0		0		0
Level 2 | Assets | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0		0		0
Level 2 | Goodwill | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill	0					0
Level 2 | Nonmarketable equity investments | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets		0		0
Level 2 | Repossessed and foreclosed assets | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	0	0		0		0
Level 3 | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans held-for-sale, net	143	185		185		143
Level 3 | Assets | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	552	243		243		552
Level 3 | Goodwill | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill	362					362
Level 3 | Nonmarketable equity investments | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets		0		0
Level 3 | Repossessed and foreclosed assets | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	8	8		8		8
Commercial | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	39	50		50		39
Lower-of-cost-or-fair-value reserve, valuation reserve, or cumulative adjustments	(65)	(77)		(77)		(65)
Commercial | Level 1 | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	0	0		0		0
Commercial | Level 2 | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	0	0		0		0
Commercial | Level 3 | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	39	50		50		39
Automotive | Commercial | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	13	23		23		13
Lower-of-cost-or-fair-value reserve, valuation reserve, or cumulative adjustments	(2)	(10)		(10)		(2)
Automotive | Commercial | Level 1 | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	0	0		0		0
Automotive | Commercial | Level 2 | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	0	0		0		0
Automotive | Commercial | Level 3 | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	13	23		23		13
Other | Commercial | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	26	27		27		26
Lower-of-cost-or-fair-value reserve, valuation reserve, or cumulative adjustments	(63)	(67)		(67)		(63)
Other | Commercial | Level 1 | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	0	0		0		0
Other | Commercial | Level 2 | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	0	0		0		0
Other | Commercial | Level 3 | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivables and loans, net	$ 26	$ 27		$ 27		$ 26