Proposition 1
Tag 0A78, permanent. Cite it as [Bourbaki, Tag 0A78].
Lie Groups and Lie Algebras, chapter III, § 1. Lie groups
A Lie group is a complete metrizable topological group.
Since admits an open neighbourhood homeomorphic to an open ball of a normed space, admits a countable fundamental system of neighbourhoods whose intersection is . Hence is metrizable (General Topology, Chapter III, § 1, Corollary to Proposition 2 and Chapter IX, § 3, Proposition 1). By Lemma 1, there exists a neighbourhood of which is complete under the right uniform structure and hence is complete (General Topology, Chapter III, § 3, Proposition 4).
Bourbaki puts the proof directly after the statement, so what is above is the statement and its proof together.