Investment Securities (Narrative) (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Schedule of Investments [Line Items]
Interest receivable	$ 43,600,000		$ 42,500,000
Held-to-maturity debt securities	7,680,075,000		7,074,797,000
Held-to-maturity investment securities in non-accrual status	0		0
Investment securities available-for-sale, at fair value	8,601,141,000		$ 8,959,729,000
Equity Securities, FV-NI, Realized Loss	(12,400,000)	$ (20,500,000)
Total Loss Recognized, Portion Included In Provision For Credit Losses	2,600,000	3,800,000
Decrease in unrealized losses	31,300,000
Total Loss Recognized, Portion Not Included In Provision For Credit Losses	(9,800,000)	$ (16,700,000)
Callable
Schedule of Investments [Line Items]
Held-to-maturity debt securities	900,000,000
Investment securities available-for-sale, at fair value	$ 2,600,000,000