ORD
Chicago O'Hare International is only 25 minutes Northeast of The Westin. It's the larger of the two airports and is a major hub for American Airlines and United Airlines. You'll also find Frontier and Spirit have a strong presence here.
MDW
Chicago Midway International is a tiny bit further at 35 minutes from the Westin, this time from the Southeast. It's smaller than O'Hare but in many cities it could be considered pretty large. Here you'll find Southwest and Delta.