Business Segment Information - Schedule of Segment Reporting Information, by Segment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Segment Reporting Information [Line Items]
Net interest income	$ 649	$ 340
Provision (benefit) for credit losses	464	(11)
Net interest income after provision for credit losses	185	351
Noninterest income	850	137
Noninterest expenses	810	297
Income before income taxes	225	191
Income tax (benefit) expense	(46)	44
Net income	271	147
Total loans and leases	65,524	33,181	$ 32,372
Total deposits	91,597	47,331	51,406
Operating lease equipment, net	7,972	0	$ 0
Operating Segments | General Banking
Segment Reporting Information [Line Items]
Net interest income	437	344
Provision (benefit) for credit losses	(15)	(11)
Net interest income after provision for credit losses	452	355
Noninterest income	123	110
Noninterest expenses	409	290
Income before income taxes	166	175
Income tax (benefit) expense	40	40
Net income	126	135
Total loans and leases	38,778	32,580
Total deposits	85,469	47,277
Operating lease equipment, net	0	0
Operating Segments | Commercial Banking
Segment Reporting Information [Line Items]
Net interest income	207	4
Provision (benefit) for credit losses	(34)	0
Net interest income after provision for credit losses	241	4
Noninterest income	112	0
Noninterest expenses	191	1
Income before income taxes	162	3
Income tax (benefit) expense	41	1
Net income	121	2
Total loans and leases	26,672	601
Total deposits	4,687	53
Operating lease equipment, net	721	0
Operating Segments | Rail
Segment Reporting Information [Line Items]
Net interest income	(19)	0
Provision (benefit) for credit losses	0	0
Net interest income after provision for credit losses	(19)	0
Noninterest income	162	0
Noninterest expenses	100	0
Income before income taxes	43	0
Income tax (benefit) expense	11	0
Net income	32	0
Total loans and leases	67	0
Total deposits	13	0
Operating lease equipment, net	7,251	0
Corporate
Segment Reporting Information [Line Items]
Net interest income	24	(8)
Provision (benefit) for credit losses	513	0
Net interest income after provision for credit losses	(489)	(8)
Noninterest income	453	27
Noninterest expenses	110	6
Income before income taxes	(146)	13
Income tax (benefit) expense	(138)	3
Net income	(8)	10
Total loans and leases	7	0
Total deposits	1,428	1
Operating lease equipment, net	$ 0	$ 0