Securities-Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Securities (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Gain (Loss) on Investments [Line Items]
Fair value	$ 106,723	$ 101,008
Available-for-sale
Gain (Loss) on Investments [Line Items]
Fair value	94,878	92,619
Government Sponsored and Guaranteed Entities, and Sovereign Debt Securities | Available-for-sale
Gain (Loss) on Investments [Line Items]
Fair value	$ 10,200	$ 9,400