Fair Value Measurements (Narrative) (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Jan. 11, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Broker dealer deposit program, fair value	$ 2,500,000,000
Unused commitments to extend credit	11,705,267,000	$ 12,563,441,000
Loans transferred to held for sale, fair value	239,300,000	3,900,000
Loans in process of foreclosure	9,100,000
Value under fair value options	323,000	2,610,000
Write-ups due to observable price changes	1,700,000
Write-downs due to impairment	(500,000)
interLINK
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Contingent consideration			$ 16,000,000
Fair Value, Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets	5,600,000	9,100,000
Rabbi Trust
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets	9,200,000	9,200,000
Alternative investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets	27,900,000	29,800,000
Carrying amount of alternative investments	1,200,000	900,000
Remaining unfunded commitment	0
Write-down	300,000
Alternative investments carrying amount	38,600,000	35,900,000
Alternative investments | Fair Value, Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unused commitments to extend credit	55,300,000	53,100,000
Unused commitments to extend credit, fair value	$ 1,400,000	$ 7,900,000