Originally Posted by JS
You could take NW via DTW to ORD or MDW from JFK in less than four hours.
Don't change airports unless absolutely necessary.
As long as its before 4pm, just get a cab around $22 inc Tip [GBP12]
I have done it faster from AA at JFK to AA at LGA, i.e.[ 25 minutes] than from Terminal 4 to Terminal 3 at Heathrow.