Fair Values of Assets and Liabilities - Estimated Fair Values of Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012		Sep. 30, 2012	Dec. 31, 2011
Financial Assets
Cash and due from banks	$ 11,615		$ 8,252		$ 9,382	$ 13,962
Investment securities held-to-maturity	36,904	[1]	34,389	[1]
Financial Liabilities
Deposits	261,716		249,183
Long-term debt	18,750		25,516
Carrying Amount [Member]
Financial Assets
Cash and due from banks	11,615		8,252
Federal funds sold and securities purchased under resale agreements	259		437
Investment securities held-to-maturity	36,904		34,389
Loans held for sale	14		19
Loans	227,027		218,765
Other financial instruments	2,149		7,367
Financial Liabilities
Deposits	261,716		249,183
Short-term borrowings	25,364		25,901
Long-term debt	18,750		25,516
Fair Value [Member]
Financial Assets
Cash and due from banks	11,615		8,252
Federal funds sold and securities purchased under resale agreements	259		437
Investment securities held-to-maturity	36,632		34,952
Loans held for sale	14		19
Loans	228,087		220,354
Other financial instruments	2,166		7,385
Financial Liabilities
Deposits	261,792		249,594
Short-term borrowings	25,307		25,917
Long-term debt	19,216		26,205
Fair Value [Member] | Level 1 [Member]
Financial Assets
Cash and due from banks	11,615		8,252
Federal funds sold and securities purchased under resale agreements
Investment securities held-to-maturity	2,912		2,984
Loans held for sale
Loans
Other financial instruments
Financial Liabilities
Deposits
Short-term borrowings
Long-term debt
Fair Value [Member] | Level 2 [Member]
Financial Assets
Cash and due from banks
Federal funds sold and securities purchased under resale agreements	259		437
Investment securities held-to-maturity	33,611		31,845
Loans held for sale
Loans
Other financial instruments	1,166		1,228
Financial Liabilities
Deposits	261,792		249,594
Short-term borrowings	25,307		25,917
Long-term debt	19,216		26,205
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	109		123
Loans held for sale	14		19
Loans	228,087		220,354
Other financial instruments	1,000		6,157
Financial Liabilities
Deposits
Short-term borrowings
Long-term debt

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