Grammatically, いいかなあ= いい+かな.
かな(often pronounced なあ、なー、なぁ) is an ending particle that adds emotion of question.
As other responses are pointing, if the speaker is talking to the listener, there is a nuance of restraint and hesitation to ask. The speaker is expecting someone would answer, but trying not to sound asking directly.
It's also used without listener like Ryota-san says.
かな itself is made from ending particle か(question) and な(wonder).