Business Combinations - Narrative (Details) $ / shares in Units, $ in Millions				12 Months Ended
	Apr. 04, 2023 USD ($)	Mar. 27, 2023 USD ($) $ / shares shares	Jan. 03, 2022 USD ($) $ / shares shares	Dec. 31, 2023 USD ($) $ / shares	Dec. 31, 2022 USD ($) $ / shares	Dec. 31, 2021 USD ($)
Business Acquisition [Line Items]
Net interest income				$ 6,712	$ 2,946	$ 1,390
Noninterest income				12,075	2,136	508
Net income				11,466	1,098	547
Gain on acquisition				9,808	431	0
Initial PCD ALLL			$ 272	220
Acquisition-related expenses				470	231	29
Operating Segments | Silicon Valley Bridge Bank Segment
Business Acquisition [Line Items]
Net interest income				1,946	0	0
Noninterest income				478	0	0
Net income				$ 530	0	$ 0
Operating Segments | CIT Group Inc.
Business Acquisition [Line Items]
Net interest income					1,750
Noninterest income					1,240
Net income					587
FDIC Credit Facility
Business Acquisition [Line Items]
FDIC advances, maximum amount available		$ 70,000
Purchase Money Note
Business Acquisition [Line Items]
Debt instrument, term		5 years
Principal amount		$ 36,070
Notes payable, fair value disclosure		35,810
SVB
Business Acquisition [Line Items]
Total assets acquired		107,539
Loans and leases		68,468
Cash and interest-earning deposits at banks		35,310
Total liabilities assumed		61,423
Deposits		56,014
Assets acquired, discount		16,450
Business combination, financing receivable acquired, amount covered by share-loss agreement		$ 60,000
Business combination, financing receivable acquired, amount covered by share-loss agreement, coverage percentage for loss up to $5 billion		0.00%
Business combination, financing receivable acquired, amount covered by share-loss agreement, coverage percentage for loss in excess of $5 billion		$ 5,000
Business combination, financing receivable acquired, above threshold amount covered by share-loss agreement, percentage		50.00%
Share-Loss Agreement, reimbursement percentage		50.00%
Share-Loss Agreement, term		5 years
Share-Loss Agreement, reimbursement term		8 years
Loans funded after acquisition date, loss share term		1 year
Share-Loss Agreement, true-up payment term		45 days
True-up amount		$ 1,500
Cash settled value appreciation instrument issued and issuable (in shares) | shares		5,000,000
Number of trading days		2 days
Cash settled value appreciation instrument, threshold amount (in dollars per share) | $ / shares		$ 582.55
Cash settled value appreciation instrument, maximum amount		$ 500
Payment to acquire business, value appreciation instrument exercised	$ 500
Preliminary gain on acquisition, after income taxes		9,808
Deferred tax liabilities		3,364
UPB		71,287
Purchase accounting adjustment of discount		2,300
Gain on acquisition		13,172
SVB | Non-PCD
Business Acquisition [Line Items]
Loans and leases acquired, FV		66,420
UPB		$ 68,719
SVB | FDIC Credit Facility
Business Acquisition [Line Items]
FHLB, advances, interest rate		0.00%
SVB | Secured Debt | FDIC Credit Facility | Secured Overnight Financing Rate
Business Acquisition [Line Items]
Basis spread on variable rate		0.25%
SVB | Purchase Money Note
Business Acquisition [Line Items]
Debt instrument, term		5 years
Debt instrument, face amount		$ 35,000
SVB | Purchase Money Note | Secured Debt
Business Acquisition [Line Items]
Debt instrument, stated interest rate		3.50%
CIT Group Inc.
Business Acquisition [Line Items]
Total assets acquired			53,775
Loans and leases			32,714
Cash and interest-earning deposits at banks			3,060
Total liabilities assumed			47,392
Deposits			39,428
Deferred tax liabilities			300
UPB			33,092
Gain on acquisition			431		431
CIT Group Inc. | Provision For Credit Losses
Business Acquisition [Line Items]
Net income					$ 513
CIT Group Inc. | Non-PCD
Business Acquisition [Line Items]
UPB			$ 29,542
Class A
Business Acquisition [Line Items]
Common stock, par value (in dollars per share) | $ / shares				$ 1	$ 1
Class A | CIT Group Inc.
Business Acquisition [Line Items]
Common stock, terms of conversion, conversion ratio			0.062
Business acquisition, equity interest Issued or issuable (in shares) | shares			6,140,010
CIT Group Inc.
Business Acquisition [Line Items]
Common stock, par value (in dollars per share) | $ / shares			$ 0.01