Business Segment Information - Schedule of Segment Reporting Information, by Segment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Segment Reporting Information [Line Items]
Net interest income	$ 700	$ 346	$ 1,349	$ 686
(Benefit) provision for credit losses	42	(20)	506	(31)
Net interest income after provision for credit losses	658	366	843	717
Noninterest income	424	133	1,274	270
Noninterest expenses	745	300	1,555	597
Income (loss) before income taxes	337	199	562	390
Income tax expense (benefit)	82	46	36	90
Net income (loss)	255	153	526	300
Total loans and leases	67,735	32,690	67,735	32,690	$ 32,372
Total deposits	89,329	48,411	89,329	48,411	51,406
Operating lease equipment, net	7,971	0	7,971	0	$ 0
Operating Segments | General Banking
Segment Reporting Information [Line Items]
Net interest income	467	363	904	707
(Benefit) provision for credit losses	7	(21)	(8)	(32)
Net interest income after provision for credit losses	460	384	912	739
Noninterest income	125	104	248	214
Noninterest expenses	390	289	799	579
Income (loss) before income taxes	195	199	361	374
Income tax expense (benefit)	40	46	80	86
Net income (loss)	155	153	281	288
Total loans and leases	40,444	32,033	40,444	32,033
Total deposits	83,535	48,344	83,535	48,344
Operating lease equipment, net	0	0	0	0
Operating Segments | Commercial Banking
Segment Reporting Information [Line Items]
Net interest income	204	4	411	8
(Benefit) provision for credit losses	35	1	1	1
Net interest income after provision for credit losses	169	3	410	7
Noninterest income	130	0	242	0
Noninterest expenses	180	1	371	2
Income (loss) before income taxes	119	2	281	5
Income tax expense (benefit)	24	0	65	1
Net income (loss)	95	2	216	4
Total loans and leases	27,220	657	27,220	657
Total deposits	4,449	66	4,449	66
Operating lease equipment, net	724	0	724	0
Operating Segments | Rail
Segment Reporting Information [Line Items]
Net interest income	(18)	0	(37)	0
(Benefit) provision for credit losses	0	0	0	0
Net interest income after provision for credit losses	(18)	0	(37)	0
Noninterest income	160	0	322	0
Noninterest expenses	111	0	211	0
Income (loss) before income taxes	31	0	74	0
Income tax expense (benefit)	7	0	18	0
Net income (loss)	24	0	56	0
Total loans and leases	71	0	71	0
Total deposits	11	0	11	0
Operating lease equipment, net	7,247	0	7,247	0
Corporate
Segment Reporting Information [Line Items]
Net interest income	47	(21)	71	(29)
(Benefit) provision for credit losses	0	0	513	0
Net interest income after provision for credit losses	47	(21)	(442)	(29)
Noninterest income	9	29	462	56
Noninterest expenses	64	10	174	16
Income (loss) before income taxes	(8)	(2)	(154)	11
Income tax expense (benefit)	11	0	(127)	3
Net income (loss)	(19)	(2)	(27)	8
Total loans and leases	0	0	0	0
Total deposits	1,334	1	1,334	1
Operating lease equipment, net	$ 0	$ 0	$ 0	$ 0