SAN FRANCISCO--(BUSINESS WIRE)--McKesson Corporation (NYSE:MCK) today reaffirmed its earnings guidance for the fiscal year ending March 31, 2016 and the underlying key assumptions provided in its press release of May 12, 2015. McKesson is hosting its Investor Day today in Boston, Massachusetts. A webcast of the presentation is available through McKesson’s website, www.mckesson.com, live from 9:00 AM to 1:00 PM ET today and on replay afterwards. Shareholders are encouraged to review McKesson’s S