Fair Values of Assets and Liabilities - Estimated Fair Values of Financial Instruments (Detail) - USD ($) $ in Millions		Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Financial Assets
Cash and due from banks		$ 10,450	$ 10,654	$ 6,183	$ 8,477
Investment securities held-to-maturity	[1]	44,690	44,974
Financial Liabilities
Deposits		295,264	282,733
Long-term debt		32,504	32,260
Carrying Amount [Member]
Financial Assets
Cash and due from banks		10,450	10,654
Federal funds sold and securities purchased under resale agreements		233	118
Investment securities held-to-maturity		44,690	44,974
Loans held for sale		43	18
Loans		250,714	243,735
Other financial instruments		2,262	2,187
Financial Liabilities
Deposits		295,264	282,733
Short-term borrowings		26,069	29,184
Long-term debt		32,504	32,260
Other Liabilities		1,442	1,231
Fair Value [Member]
Financial Assets
Cash and due from banks		10,450	10,654
Federal funds sold and securities purchased under resale agreements		233	118
Investment securities held-to-maturity		45,051	45,140
Loans held for sale		43	18
Loans		252,464	245,424
Other financial instruments		2,270	2,193
Financial Liabilities
Deposits		295,235	282,708
Short-term borrowings		25,851	28,973
Long-term debt		33,021	32,659
Other Liabilities		1,442	1,231
Fair Value [Member] | Level 1 [Member]
Financial Assets
Cash and due from banks		10,450	10,654
Investment securities held-to-maturity		2,312	1,928
Fair Value [Member] | Level 2 [Member]
Financial Assets
Federal funds sold and securities purchased under resale agreements		233	118
Investment securities held-to-maturity		42,658	43,124
Other financial instruments		921	924
Financial Liabilities
Deposits		295,235	282,708
Short-term borrowings		25,851	28,973
Long-term debt		33,021	32,659
Fair Value [Member] | Level 3 [Member]
Financial Assets
Investment securities held-to-maturity		81	88
Loans held for sale		43	18
Loans		252,464	245,424
Other financial instruments		1,349	1,269
Financial Liabilities
Other Liabilities		$ 1,442	$ 1,231

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