Investment Securities - Amount of Interest Income from Taxable and Non-Taxable Investment Securities (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Taxable And Tax Exempt Interest Income [Abstract]
Taxable	$ 357	$ 369	$ 1,029	$ 1,166
Non-taxable	63	69	193	210
Total interest income from investment securities	$ 420	$ 438	$ 1,222	$ 1,376