Original links are included though some may have expired.

The Numbers:

Savings deposits at Japan Post: $1.7 trillion^*
Savings deposits at all U.S. commercial banks: $5.9 trillion
Savings deposits at all other private banks, world^**: $7.1 trillion

^* Does not include $1.3 trillion in insurance assets.
^** Excludes deposits in state-owned institutions like Japan Post or China's four state-owned banks.

What They Mean:

Each year, the world's families, businesses, and governments combine to put 22 percent of their income in the bank. Among rich countries, Japan is the largest saver: its savings rate is 28 percent of "gross national income." Europe's savings rate is about 21 percent, though Britain is quite low at 14.8 percent. Developing countries save more: low- to middle-income Asian countries save 33 percent to 38 percent of their national income, Africa 22 percent, the Middle East 30 percent, and Latin America 21 percent. Savings in the United States, by contrast, hovers above 13 percent -- and in net terms is approaching zero -- which is the lowest rate of the last 75 years.

As the United States looks for lenders to cover government deficits, heavy savers send some money over to buy Treasury notes and puzzle over what to do with the rest. The largest pot of savings in the world, along with the world's largest financial asset-management question mark, is found in the back offices of the Japanese Postal Service.

Like the postal services of the United States, Britain, South Africa, Brazil, etc., Japan Post delivers mail. Unlike other postal agencies, it accepts savings deposits, sells insurance, and pays its subscribers' utility bills electronically. Thus Japan Post has a huge pile of money: $1.7 trillion in savings deposits and $1.3 trillion in insurance. The savings deposits alone are triple the deposits of the largest U.S. bank and amount to a quarter of the $5.9 trillion now deposited in all FDIC-insured U.S. banks combined. Apart from lending to carefree Americans, Japan's governments have been using the postal accounts to build roads (with one-fiftieth the land area of the United States, Japan is said to use as much concrete each year as America), pay for a postal workforce 10 percent bigger than the Japan Self-Defense Forces, and manage 24,700 post offices nationwide.

Some are not satisfied with this use of money. Hoping to promote more lending to entrepreneurial businesses and less to road-builders, and to develop a more efficient financial system generally, Japan's Prime Minister and Diet supporters hope to break the postal behemoth into four private businesses by 2017: (1) a mail delivery company, (2) a postal savings firm, (3) an insurance group, and (4) a company for over-the-counter services. The plan would complete this job by 2017.

Further Reading:

Prime Minister Koizumi speaks to the Diet on postal reform:
http://www.kantei.go.jp/foreign/koizumispeech/
2005/09/26shoshin_e.html

Japan Post manages 260,000 employees and 24,700 post offices; on average that's one every six square miles. It seems to save lots of money on website development:
http://www.japanpost.jp/english/index.html

Views of Postal Savings reform from the U.S. Treasury:
http://www.treas.gov/press/releases/js2954.htm

and Foreign Press Center Japan: http://www.fpcj.jp/e/mres/japanbrief/jb_519.html

IMF statistics on world savings and investment (pg. 275):
http://www.internationalmonetaryfund.com/external/
pubs/ft/weo/2005/02/pdf/statappx.pdf

U.S. gross and net savings (since 1929) from the Bureau of Economic Analysis:
http://www.bea.gov/bea/dn/nipaweb/TableView.asp?
SelectedTable=120&FirstYear=2003&LastYear=2005&Freq=Qtr

Meanwhile: An almost equally big job is underway in China. China is implementing WTO financial-services agreements, trying to catch a runaway bank manager said to have absconded with $485 million, and has spent over $60 billion to recapitalize banks rich in non-performing loans but not in assets. (NPL's were said to total 25 percent of Chinese GDP two years ago; Standard & Poor's estimates the current level at $700 billion, which would still be about 25 percent of GDP.) China is also trying to privatize its four major state banks -- Industrial & Commercial Bank of China (ICBC), China Construction Bank (CCB), Bank of China, and Agricultural Bank of China -- which together have 116,000 branches, 1.4 million employees and a bit less than 70 percent of national savings deposits. COF Asia explains (free subscription required) and has more info about international banks:
http://www.cfoasia.com/archives/200512-11.htm

FDIC explains the implications of Chinese banking reform:
http://www.fdic.gov/bank/analytical/banking/
2005nov/article1.html

A list of America's top 150 banks, based on deposit holdings, as of spring 2005:
http://onlinebankingreport.com/resources/100.html