Consolidated Balance Sheet [Unaudited] (Parenthetical) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Statement Of Financial Position [Abstract]
Held-to-maturity securities, fair value	$ 35,183,000,000	$ 34,952,000,000
Held-to-maturity securities, pledged as collateral	994,000,000	1,482,000,000
Available-for-sale securities pledged as collateral	1,497,000,000	2,042,000,000
Mortgage loans, carried at fair value	7,562,000,000	7,957,000,000
Trading securities at fair value pledged as collateral	63,000,000	47,000,000
Time deposits	$ 100,000	$ 100,000
Common stock, par value	$ 0.01	$ 0.01
Common stock, share-authorized (actual number of shares)	4,000,000,000	4,000,000,000
Common stock, shares issued (actual number of shares)	2,125,725,742	2,125,725,742
Treasury stock, shares(actual number of shares)	267,239,988	256,294,227