Walmart is in preliminary talks to buy health insurer Humana, according to people familiar with the matter, the Wall Street Journal reported this week. The proposal would be the latest in a series of recent proposals involving retailers and others that could change the health care landscape. For example, Amazon, Berkshire Hathaway and JPMorgan Chase & Co. in January announced plans to create an independent company to address health care for their U.S. employees, and CVS Health has proposed acquiring health insurance company Aetna.