Business Combinations - Narrative (Details) $ / shares in Units, $ in Millions				3 Months Ended		6 Months Ended	9 Months Ended
	Apr. 04, 2023 USD ($)	Mar. 27, 2023 USD ($) $ / shares	Jan. 03, 2022 USD ($) $ / shares shares	Sep. 30, 2023 USD ($) $ / shares	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) $ / shares	Sep. 30, 2023 USD ($) $ / shares	Sep. 30, 2022 USD ($)	Dec. 31, 2022 $ / shares
Business Acquisition [Line Items]
Net interest income				$ 1,990	$ 795		$ 4,801	$ 2,144
Noninterest income				615	433		11,532	1,707
Net income				752	315		10,952	841
Gain on acquisition				12	0		9,891	431
Operating Segments | Silicon Valley Banking
Business Acquisition [Line Items]
Net interest income				635	0		1,335	0
Noninterest income				151	0		334	0
Net income				$ 157	$ 0		$ 381	$ 0
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		61,340
Deposits		56,014
Assets acquired, discount		16,450
Business combination, consideration transferred, liabilities incurred		35,808
Cash settled value appreciation instrument issued and issuable		$ 5
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
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
Preliminary gain on acquisition, after income taxes, period increase						$ 67
Preliminary gain on acquisition, after income taxes		9,891
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]
Debt instrument, term		5 years
FDIC advances, maximum amount available		$ 70,000
Debt instrument, period following acquisition date		2 years
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 | Secured Debt
Business Acquisition [Line Items]
Debt instrument, term		5 years
Business combination, consideration transferred, liabilities incurred		$ 36,000
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
Gain on acquisition			$ 431
Class A Common Stock
Business Acquisition [Line Items]
Common stock, par value (in dollars per share) | $ / shares				$ 1		$ 1	$ 1		$ 1
Class A Common Stock | 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