10 million and 10 billion is right.
The following rules apply to the plurals of numerical terms such as dozen, score, hundred, thousand, million, and similar:
1) When modified by a number, the plural has no -s added. Hence one hundred, two million, four score, etc. (The resulting quantitative expressions are treated as numbers, in that they can modify nouns directly:
e.g. three dozen eggs, although ''of'' is used before pronouns or definite noun phrases: three dozen of them/of those eggs.)
2) When not modified by a number, the plural takes -s as usual, and the resulting expression is not a number (it requires 'of' if modifying a noun):
e.g. I have hundreds, dozens of complaints, the thousands of people affected.
3) When the modifier is a vaguer expression of number, either pattern may be followed: several hundred (people) or several hundreds (of people).
4) When the word has a specific meaning rather than being a simple expression of quantity, it is pluralized as an ordinary noun:
e.g. Last season he scored eight hundreds [=scores of at least 100 runs]. The same applies to other numbers: My phone number consists of three fives and four sixes.