Fix markup in decimal.rst.
diff --git a/Doc/library/decimal.rst b/Doc/library/decimal.rst
index 2697026..d22ea4b 100644
--- a/Doc/library/decimal.rst
+++ b/Doc/library/decimal.rst
@@ -365,7 +365,7 @@
creating a Decimal instance from a string.
.. versionchanged:: 2.7
- The argument to the constructor is now permitted to be a :float:`instance`.
+ The argument to the constructor is now permitted to be a :class:`float` instance.
Decimal floating point objects share many properties with the other built-in
numeric types such as :class:`float` and :class:`int`. All of the usual math