Business Segment Information - Schedule of Segment Reporting Information, by Segment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Segment Reporting Information [Line Items]
Net interest income (expense)	$ 795	$ 347	$ 2,144	$ 1,033
(Benefit) provision for credit losses	60	(1)	566	(32)
Net interest income (expense) after provision for credit losses	735	348	1,578	1,065
Noninterest income	433	124	1,707	394
Noninterest expense	760	314	2,315	911
Income (loss) before income taxes	408	158	970	548
Income tax expense (benefit)	93	34	129	124
Net income (loss)	315	124	841	424
Loans and leases	69,790	32,516	69,790	32,516	$ 32,372
Deposits	87,553	50,065	87,553	50,065	51,406
Operating lease equipment, net	7,984	0	7,984	0	$ 0
Operating Segments | General Banking
Segment Reporting Information [Line Items]
Net interest income (expense)	495	363	1,400	1,071
(Benefit) provision for credit losses	2	(1)	(7)	(32)
Net interest income (expense) after provision for credit losses	493	364	1,407	1,103
Noninterest income	118	110	365	325
Noninterest expense	410	295	1,210	875
Income (loss) before income taxes	201	179	562	553
Income tax expense (benefit)	55	38	134	125
Net income (loss)	146	141	428	428
Loans and leases	41,693	31,849	41,693	31,849
Deposits	82,730	49,992	82,730	49,992
Operating lease equipment, net	0	0	0	0
Operating Segments | Commercial Banking
Segment Reporting Information [Line Items]
Net interest income (expense)	230	5	641	12
(Benefit) provision for credit losses	58	0	60	0
Net interest income (expense) after provision for credit losses	172	5	581	12
Noninterest income	133	0	376	0
Noninterest expense	186	1	557	3
Income (loss) before income taxes	119	4	400	9
Income tax expense (benefit)	25	1	90	2
Net income (loss)	94	3	310	7
Loans and leases	28,023	667	28,023	667
Deposits	3,682	73	3,682	73
Operating lease equipment, net	736	0	736	0
Operating Segments | Rail
Segment Reporting Information [Line Items]
Net interest income (expense)	(20)	0	(58)	0
(Benefit) provision for credit losses	0	0	0	0
Net interest income (expense) after provision for credit losses	(20)	0	(58)	0
Noninterest income	170	0	493	0
Noninterest expense	110	0	320	0
Income (loss) before income taxes	40	0	115	0
Income tax expense (benefit)	10	0	28	0
Net income (loss)	30	0	87	0
Loans and leases	74	0	74	0
Deposits	14	0	14	0
Operating lease equipment, net	7,248	0	7,248	0
Corporate
Segment Reporting Information [Line Items]
Net interest income (expense)	90	(21)	161	(50)
(Benefit) provision for credit losses	0	0	513	0
Net interest income (expense) after provision for credit losses	90	(21)	(352)	(50)
Noninterest income	12	14	473	69
Noninterest expense	54	18	228	33
Income (loss) before income taxes	48	(25)	(107)	(14)
Income tax expense (benefit)	3	(5)	(123)	(3)
Net income (loss)	45	(20)	16	(11)
Loans and leases	0	0	0	0
Deposits	1,127	0	1,127	0
Operating lease equipment, net	$ 0	$ 0	$ 0	$ 0