Investment Securities (Narrative) (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2022	Jan. 31, 2022	Dec. 31, 2021
Schedule of Investments [Line Items]
Increase in available for sale debt securities	$ 4,500,000,000
Interest receivable		$ 41,900,000		$ 7,500,000
Held-to-maturity debt securities		6,362,458,000		6,198,339,000
Held-to-maturity investment securities in non-accrual status		0		0
Investment securities available-for-sale, at fair value		8,744,897,000		$ 4,234,854,000
Sterling
Schedule of Investments [Line Items]
Investment securities available-for-sale			$ 4,429,948,000
Callable
Schedule of Investments [Line Items]
Held-to-maturity debt securities		700,000,000
Investment securities available-for-sale, at fair value		$ 3,500,000,000