Fair Value Measurements - Carrying Amounts and Estimated Fair Value for Financial Instrument Assets (Liabilities) (Detail) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Financial assets:
Interest-bearing deposits at banks	$ 18,873	$ 28,069
Investment securities held to maturity	34,051	26,897
Net loans and leases	133,397	131,939
Financial liabilities:
Long-term borrowings	12,605	8,201
Level 1
Financial assets:
Cash and cash equivalents	1,749	1,668
Interest-bearing deposits at banks	0	0
Investment securities held to maturity	0	0
Net loans and leases	0	0
Financial liabilities:
Time deposits	0	0
Short-term borrowings	0	0
Long-term borrowings	0	0
Level 2
Financial assets:
Cash and cash equivalents	160	63
Interest-bearing deposits at banks	18,873	28,069
Investment securities held to maturity	12,909	14,262
Net loans and leases	6,806	7,240
Financial liabilities:
Time deposits	14,463	20,715
Short-term borrowings	1,060	5,316
Long-term borrowings	12,754	8,107
Level 3
Financial assets:
Cash and cash equivalents	0	0
Interest-bearing deposits at banks	0	0
Investment securities held to maturity	46	46
Net loans and leases	124,528	121,898
Financial liabilities:
Time deposits	0	0
Short-term borrowings	0	0
Long-term borrowings	0	0
Carrying Amount
Financial assets:
Cash and cash equivalents	1,909	1,731
Interest-bearing deposits at banks	18,873	28,069
Investment securities held to maturity	14,195	15,330
Net loans and leases	133,397	131,939
Financial liabilities:
Time deposits	14,476	20,759
Short-term borrowings	1,060	5,316
Long-term borrowings	12,605	8,201
Estimated Fair Value
Financial assets:
Cash and cash equivalents	1,909	1,731
Interest-bearing deposits at banks	18,873	28,069
Investment securities held to maturity	12,955	14,308
Net loans and leases	131,334	129,138
Financial liabilities:
Time deposits	14,463	20,715
Short-term borrowings	1,060	5,316
Long-term borrowings	$ 12,754	$ 8,107