Parent Company Condensed Financial Information - Schedule of Condensed Statement of Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		3 Months Ended								6 Months Ended		9 Months Ended		12 Months Ended
		Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2024	Jun. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Net financing revenue and other interest income														$ 6,014	$ 6,221	$ 6,850
Total other revenue														2,167	2,013	1,578
Total net revenue														8,181	8,234	8,428
Provision for credit losses														2,166	1,968	1,399
Total noninterest expense														5,179	5,163	4,687
Income (loss) from continuing operations before income tax expense														836	1,103	2,342
Income tax benefit from continuing operations		$ 0	$ 67	$ 60	$ 40	$ 10	$ (51)	$ 96	$ 89					167	144	627
Net income from continuing operations														669	959	1,715	[1]
Loss from discontinued operations, net of tax	[1]													(1)	(2)	(1)
Net income		108	198	219	143	62	285	311	299	$ 362	$ 610	$ 560	$ 895	668	957	1,714
Other comprehensive (loss) income, net of tax														(108)	243	(3,901)
Comprehensive income (loss)		$ (423)	$ 814	$ 199	$ (30)	$ 1,011	$ (617)	$ 224	$ 582					560	1,200	(2,187)
Parent company
Net financing revenue and other interest income														(884)	(945)	(1,000)
Dividends from bank subsidiaries														1,200	1,350	3,150
Dividends from nonbank subsidiaries														0	250	1
Total other revenue														134	169	103
Total net revenue														450	824	2,254
Provision for credit losses														8	(14)	(32)
Total noninterest expense														473	466	665
Income (loss) from continuing operations before income tax expense														(31)	372	1,621
Income tax benefit from continuing operations														(327)	(408)	(253)
Net income from continuing operations														296	780	1,874
Loss from discontinued operations, net of tax														(1)	(2)	(1)
Equity in undistributed earnings of subsidiaries														373	179	(159)
Net income														668	957	1,714
Other comprehensive (loss) income, net of tax														(108)	243	(3,901)
Comprehensive income (loss)														$ 560	$ 1,200	$ (2,187)

[1] Figures in the table may not recalculate exactly due to rounding. Earnings per share is calculated based on unrounded numbers.