The updated projections show the average 65-year-old male is expected to live to 86.6, an increase of two years. The average woman is expected to live until 88.8, an increase of 2.4 years.

Read: How best to communicate retirement planning to female clients

In a note to investors, analysts at Moody's said the IRS was expected to require sponsors to apply the new mortality assumptions this year, but that the agency is still evaluating them and will not apply the new numbers until 2017.

"The dollar impact of this change will be substantial," wrote the analysts.

At the end of last year, the non-financial corporations that Moody's rates had a combined projected benefit obligation of $2.1 trillion.

Applying the updated mortality tables means a 6 percent, or combined $126 billion increase in those obligations.

The delay, and the $18 billion in funding obligations that sponsors will save this year, is a "credit positive." But Moody's also warned the benefit to delaying the inevitable will do little for those plans facing systemic funding issues.

"Without addressing the underlying causes of pension plan funding levels, currently languishing at 78 percent, those who fund only the minimum required are simply kicking the can down the road," wrote the analysts.

Moody's estimated the aggregate funding level at 86 percent in 2013.

Sponsors will also be able to save money on the lump-sum pension buyouts they negotiate. Longer mortality expectations increase the value of a lump sum, thus making them more expensive for sponsors.

In July, the IRS issued new rules prohibiting sponsors from offering lump-sum buyouts to retirees already receiving pension benefits.