Fair Values of Assets and Liabilities - Estimated Fair Values of Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013		Sep. 30, 2013	Dec. 31, 2012
Financial Assets
Cash and due from banks	$ 6,183		$ 8,477		$ 11,615	$ 8,252
Investment securities held-to-maturity	44,231	[1]	38,920	[1]
Financial Liabilities
Deposits	273,097		262,123
Long-term debt	30,768		20,049
Carrying Amount [Member]
Financial Assets
Cash and due from banks	6,183		8,477
Federal funds sold and securities purchased under resale agreements	168		163
Investment securities held-to-maturity	44,231		38,920
Loans held for sale	21		5
Loans	241,384		230,857
Other financial instruments	2,227		2,443
Financial Liabilities
Deposits	273,097		262,123
Short-term borrowings	29,277		26,945
Long-term debt	30,768		20,049
Other Liabilities	1,307		1,263
Fair Value [Member]
Financial Assets
Cash and due from banks	6,183		8,477
Federal funds sold and securities purchased under resale agreements	168		163
Investment securities held-to-maturity	44,094		38,368
Loans held for sale	21		5
Loans	243,700		231,480
Other financial instruments	2,233		2,463
Financial Liabilities
Deposits	273,147		262,200
Short-term borrowings	29,134		26,863
Long-term debt	31,220		20,391
Other Liabilities	1,307		1,263
Fair Value [Member] | Level 1 [Member]
Financial Assets
Cash and due from banks	6,183		8,477
Federal funds sold and securities purchased under resale agreements
Investment securities held-to-maturity	1,905		2,589
Loans held for sale
Loans
Other financial instruments
Financial Liabilities
Deposits
Short-term borrowings
Long-term debt
Other Liabilities
Fair Value [Member] | Level 2 [Member]
Financial Assets
Cash and due from banks
Federal funds sold and securities purchased under resale agreements	168		163
Investment securities held-to-maturity	42,093		35,678
Loans held for sale
Loans
Other financial instruments	944		1,080
Financial Liabilities
Deposits	273,147		262,200
Short-term borrowings	29,134		26,863
Long-term debt	31,220		20,391
Other Liabilities
Fair Value [Member] | Level 3 [Member]
Financial Assets
Cash and due from banks
Federal funds sold and securities purchased under resale agreements
Investment securities held-to-maturity	96		101
Loans held for sale	21		5
Loans	243,700		231,480
Other financial instruments	1,289		1,383
Financial Liabilities
Deposits
Short-term borrowings
Long-term debt
Other Liabilities	$ 1,307		$ 1,263

[1] Includes only collateral pledged by the Company where counterparties have the right to sell or pledge the collateral.