Fair Values of Assets and Liabilities - Estimated Fair Values of Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014		Mar. 31, 2014	Dec. 31, 2013
Financial Assets
Cash and due from banks	$ 14,072		$ 10,654		$ 7,408	$ 8,477
Investment securities held-to-maturity	45,597	[1]	44,974	[1]
Financial Liabilities
Deposits	286,601		282,733
Long-term debt	35,104		32,260
Carrying Amount [Member]
Financial Assets
Cash and due from banks	14,072		10,654
Federal funds sold and securities purchased under resale agreements	157		118
Investment securities held-to-maturity	45,597		44,974
Loans held for sale	3,035		18
Loans	241,264		243,735
Other financial instruments	2,195		2,187
Financial Liabilities
Deposits	286,601		282,733
Short-term borrowings	27,411		29,184
Long-term debt	35,104		32,260
Other Liabilities	1,191		1,231
Fair Value [Member]
Financial Assets
Cash and due from banks	14,072		10,654
Federal funds sold and securities purchased under resale agreements	157		118
Investment securities held-to-maturity	46,022		45,140
Loans held for sale	3,040		18
Loans	243,651		245,424
Other financial instruments	2,202		2,193
Financial Liabilities
Deposits	286,618		282,708
Short-term borrowings	27,235		28,973
Long-term debt	35,678		32,659
Other Liabilities	1,191		1,231
Fair Value [Member] | Level 1 [Member]
Financial Assets
Cash and due from banks	14,072		10,654
Investment securities held-to-maturity	2,004		1,928
Fair Value [Member] | Level 2 [Member]
Financial Assets
Federal funds sold and securities purchased under resale agreements	157		118
Investment securities held-to-maturity	43,932		43,124
Other financial instruments	924		924
Financial Liabilities
Deposits	286,618		282,708
Short-term borrowings	27,235		28,973
Long-term debt	35,678		32,659
Fair Value [Member] | Level 3 [Member]
Financial Assets
Investment securities held-to-maturity	86		88
Loans held for sale	3,040		18
Loans	243,651		245,424
Other financial instruments	1,278		1,269
Financial Liabilities
Other Liabilities	$ 1,191		$ 1,231

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