Comcast spends roughly $1.3 billion a year on health care for its 225,000 employees and families. : Frustrated with insurers, some large companies — including a certain cable behemoth — are shedding long-held practices and adopting a do-it-yourself approach. It isn’t headquartered in Silicon Valley, with all the venture-backed start-ups. It’s not among the corporate giants — Amazon, Berkshire Hathaway and JPMorgan Chase — that recently announced, with much fanfare, a plan to overhaul the medical-industrial complex for their employees. And it is among the most hated companies in the United States, according to many surveys on customer satisfaction. It’s Comcast.