We already know that the Foo Fighters will be playing at Wrigley Field August 29. Since the ballpark will be available for concerts during that Cubs road trip, the team has added another performer:
Live Nation announces Billy Joel to play Wrigley Field this summer again on Aug. 27. Adds to Foo Fighters, which will play stadium 8/29.— Danny Ecker (@DannyEcker) January 15, 2015
This will be Billy Joel's record 4th performance at Wrigley Field. Show not tied to the team's new live music venture w/ CBS Radio Group.— Danny Ecker (@DannyEcker) January 15, 2015
As I recall, the Cubs' music venture with CBS Radio is intended to have outdoor shows on the plaza that will be constructed to the west of the ballpark on the triangle lot. That lot will be under construction through most of 2015 as the Cubs build their new underground clubhouse. That doesn't mean CBS couldn't sponsor other shows inside Wrigley, though.
As noted, Billy Joel has played Wrigley three other times: two shows in July 2009 and one last summer. According to the Cubs website, there will be a presale for American Express cardmembers January 20 through January 23. No word yet on whether or when there will be a presale for Cubs season-ticket holders. Tickets are on sale to the general public January 24.