Following my most recent layoff I received 52 weeks salary paid out over the year, in addition to all benefits at group rates. It was based on tenure and is the maximum under under the company's plan. It was not paid as a lump sum.
Everyone laid off received 2 weeks for every year employed, up to 52 weeks.
It's not unusual at all for large corporations. It works for some, depending upon your age and individual circumstances.
(If you accept other employment, however, this separation benefit ends.)