Consolidated Balance Sheet (Unaudited) (Parenthetical) (USD $)	Jun. 30, 2013	Dec. 31, 2012
Held-to-maturity securities, fair value	$ 34,514,000,000	$ 34,952,000,000
Securities, pledged as collateral	2,200,000,000	3,500,000,000
Mortgage loans, carried at fair value	4,753,000,000	7,957,000,000
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)	281,665,410	256,294,227
Held-to-maturity Securities [Member]
Securities, pledged as collateral	1,019,000,000	1,482,000,000
Available-for-Sale Securities [Member]
Securities, pledged as collateral	1,152,000,000	2,042,000,000
Trading Securities [Member]
Securities, pledged as collateral	$ 81,000,000	$ 47,000,000