Fair Values of Assets and Liabilities - Estimated Fair Values of Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012		Mar. 31, 2012	Dec. 31, 2011
Financial Assets
Cash and due from banks	$ 6,932		$ 8,252		$ 9,561	$ 13,962
Investment securities held-to-maturity	34,716	[1]	34,389	[1]
Loans	218,961		218,905
Financial Liabilities
Deposits	248,012		249,183
Long-term debt	25,239		25,516
Carrying Amount [Member]
Financial Assets
Cash and due from banks	6,932		8,252
Federal funds sold and securities purchased under resale agreements	90		437
Investment securities held-to-maturity	34,716		34,389
Loans held for sale	157		19
Loans	218,961		218,905
Other financial instruments	7,372		7,367
Financial Liabilities
Deposits	248,012		249,183
Short-term borrowings	26,533		25,901
Long-term debt	25,239		25,516
Fair Value [Member]
Financial Assets
Cash and due from banks	6,932		8,252
Federal funds sold and securities purchased under resale agreements	90		437
Investment securities held-to-maturity	35,183		34,952
Loans held for sale	159		19
Loans	221,040		220,494
Other financial instruments	7,392		7,385
Financial Liabilities
Deposits	248,344		249,594
Short-term borrowings	26,526		25,917
Long-term debt	26,099		26,205
Fair Value [Member] | Level 1 [Member]
Financial Assets
Cash and due from banks	6,932		8,252
Investment securities held-to-maturity	3,221		2,984
Fair Value [Member] | Level 2 [Member]
Financial Assets
Federal funds sold and securities purchased under resale agreements	90		437
Investment securities held-to-maturity	31,846		31,845
Other financial instruments	1,210		1,228
Financial Liabilities
Deposits	248,344		249,594
Short-term borrowings	26,526		25,917
Long-term debt	26,099		26,205
Fair Value [Member] | Level 3 [Member]
Financial Assets
Investment securities held-to-maturity	116		123
Loans held for sale	159		19
Loans	221,040		220,494
Other financial instruments	$ 6,182		$ 6,157

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