Investment Securities - Amount of Interest Income from Taxable and Non-Taxable Investment Securities (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Taxable And Tax Exempt Interest Income [Abstract]
Taxable	$ 403	$ 328	$ 784	$ 672
Non-taxable	58	64	118	130
Total interest income from investment securities	$ 461	$ 392	$ 902	$ 802