Fair Values of Assets and Liabilities - Estimated Fair Values of Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012		Jun. 30, 2012	Dec. 31, 2011
Financial Assets
Cash and due from banks	$ 6,618		$ 8,252		$ 15,403	$ 13,962
Investment securities held-to-maturity	34,668	[1]	34,389	[1]
Financial Liabilities
Deposits	251,568		249,183
Long-term debt	19,724		25,516
Carrying Amount [Member]
Financial Assets
Cash and due from banks	6,618		8,252
Federal funds sold and securities purchased under resale agreements	183		437
Investment securities held-to-maturity	34,668		34,389
Loans held for sale	13		19
Loans	223,587		218,765
Other financial instruments	2,045		7,367
Financial Liabilities
Deposits	251,568		249,183
Short-term borrowings	25,482		25,901
Long-term debt	19,724		25,516
Fair Value [Member]
Financial Assets
Cash and due from banks	6,618		8,252
Federal funds sold and securities purchased under resale agreements	183		437
Investment securities held-to-maturity	34,514		34,952
Loans held for sale	13		19
Loans	224,714		220,354
Other financial instruments	2,064		7,385
Financial Liabilities
Deposits	251,681		249,594
Short-term borrowings	25,438		25,917
Long-term debt	20,215		26,205
Fair Value [Member] | Level 1 [Member]
Financial Assets
Cash and due from banks	6,618		8,252
Federal funds sold and securities purchased under resale agreements
Investment securities held-to-maturity	3,174		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	183		437
Investment securities held-to-maturity	31,228		31,845
Loans held for sale
Loans
Other financial instruments	1,184		1,228
Financial Liabilities
Deposits	251,681		249,594
Short-term borrowings	25,438		25,917
Long-term debt	20,215		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	112		123
Loans held for sale	13		19
Loans	224,714		220,354
Other financial instruments	880		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.