Pros
Relatively good benefits with pension. Huge company with lots of opportunity for growth. Good experience for resume. Once you're in, it's likely you'll be able to stay here for as long as you wish. There are many employees with 25+ years with the company. It's a regulated utility so chances are, the company isn't going anywhere.
Cons
Typical corporate issues - they're always trying to save money by cutting out things that are important to employees like incentives, giving the only option for high deductible health care, not paying for family/spouses to be on health care, etc. A lot of positions are being outsourced to contractors. In some departments, it's hard to move around because a lot of favoritism exists. And of course, if you didn't already know, nepotism is huge in this company. And finally, a lot of retirements are happening and the company isn't replacing those individuals. Instead, they're expecting the current workforce to handle the extra workload, expecting as many hours as it takes to get the work done, and they have no focus on live/work balance whatsoever.