Pledged Assets - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	$ 32,400,000,000		$ 32,400,000,000		$ 32,400,000,000
Fair value of accepted collateral	1,000,000,000		1,000,000,000		500,000,000
Amount of securities repledged or sold collateral	0		0		0
Average deposits maintained to meet Federal Reserve Bank reserve requirements	1,300,000,000	900,000,000	1,300,000,000	900,000,000
US Government Corporations and Agencies Securities
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	23,500,000,000		23,500,000,000		22,600,000,000
Obligations of States and Political Subdivisions
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	137,000,000		137,000,000		222,700,000
Loans
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	8,800,000,000		8,800,000,000		9,600,000,000
Collateral Requirements
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	3,500,000,000		3,500,000,000		5,000,000,000
Available for Sale Investment Securities
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	$ 865,500,000		$ 865,500,000		$ 915,300,000