How to convert "money" columns to "numeric"?

I want to convert a column named "amount", currently of type money, to type
numeric(10,2).

When I try to do this using:

ALTER TABLE transaction ALTER COLUMN amount TYPE NUMERIC(10,2);

I get:

PostgreSQL Error Code: (1)
ERROR: column "amount" cannot be cast to type "pg_catalog.numeric"

So then I figure I need to do it with SQL of the form:

ALTER TABLE transaction ALTER COLUMN amount TYPE NUMERIC(10,2) USING
<expression>;

But I can't find a conversion function or operator that will accept a
"money" column as input. For example:

ALTER TABLE transaction ALTER COLUMN amount TYPE NUMERIC(10,2) USING
to_number(amount, '99999999.99');

Evokes this error message:

PostgreSQL Error Code: (1)
ERROR: function to_number(money, "unknown") does not exist
HINT: No function matches the given name and argument types. You may need
to add explicit type casts.

And I can't seem to cast a "money" column into anything else. For example:

ALTER TABLE transaction ALTER COLUMN amount TYPE NUMERIC(10,2) USING
cast(amount as numeric);

Evokes:

PostgreSQL Error Code: (1)
ERROR: column "amount" cannot be cast to type "pg_catalog.numeric"

So I'm fresh out of ideas - other than dropping and recreating the column,
which would lose a lot of data.

~ TIA
~ Ken