Fair Values of Assets and Liabilities - Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Millions	Sep. 30, 2023		Dec. 31, 2022
Financial Assets
Cash and due from banks	$ 64,354		$ 53,542
Investment securities held-to-maturity	85,342	[1]	88,740
Loans	368,016		381,277
Financial Liabilities
Long-term debt	43,074		39,829
Carrying Amount [Member]
Financial Assets
Cash and due from banks	64,354		53,542
Federal funds sold and securities purchased under resale agreements	1,847		356
Investment securities held-to-maturity	85,342		88,740
Loans held for sale	73		351
Loans	368,016		381,277
Other	2,369		2,962
Financial Liabilities
Time deposits	53,100		32,946
Short-term borrowings	19,947		29,527
Long-term debt	43,074		39,829
Other	5,196		5,137
Fair Value [Member]
Financial Assets
Cash and due from banks	64,354		53,542
Federal funds sold and securities purchased under resale agreements	1,847		356
Investment securities held-to-maturity	70,359		77,874
Loans held for sale	73		351
Loans	356,814		368,874
Other	2,369		2,962
Financial Liabilities
Time deposits	52,934		32,338
Short-term borrowings	19,612		29,145
Long-term debt	40,377		37,622
Other	5,196		5,137
Fair Value [Member] | Level 1 [Member]
Financial Assets
Cash and due from banks	64,354		53,542
Federal funds sold and securities purchased under resale agreements	0		0
Investment securities held-to-maturity	1,283		1,293
Loans held for sale	0		0
Loans	0		0
Other	0		0
Financial Liabilities
Time deposits	0		0
Short-term borrowings	0		0
Long-term debt	0		0
Other	0		0
Fair Value [Member] | Level 2 [Member]
Financial Assets
Cash and due from banks	0		0
Federal funds sold and securities purchased under resale agreements	1,847		356
Investment securities held-to-maturity	69,076		76,581
Loans held for sale	0		0
Loans	0		0
Other	1,710		2,224
Financial Liabilities
Time deposits	52,934		32,338
Short-term borrowings	19,612		29,145
Long-term debt	40,377		37,622
Other	1,314		1,500
Fair Value [Member] | Level 3 [Member]
Financial Assets
Cash and due from banks	0		0
Federal funds sold and securities purchased under resale agreements	0		0
Investment securities held-to-maturity	0		0
Loans held for sale	73		351
Loans	356,814		368,874
Other	659		738
Financial Liabilities
Time deposits	0		0
Short-term borrowings	0		0
Long-term debt	0		0
Other	$ 3,882		$ 3,637

[1] The weighted-average maturity of total held-to-maturity investment securities was 9.2 years at December 31, 2022, with a corresponding weighted-average yield of 2.18 percent. The weighted-average maturity of total available-for-sale investment securities was 7.4 years at December 31, 2022, with a corresponding weighted-average yield of 2.94 percent.