Liabilities have hit a new all-time high at the largest corporate pension plans. 

That’s according to Russell Investments’ annual report on the performance of what it calls the $20 billion club — 19 corporations with worldwide pension liabilities exceeding $20 billion, which together account for approximately 40 percent of the pension assets and liabilities of all U.S. publicly listed corporations. 

At the beginning of 2014, the 19 “club” members had a combined pension deficit of $114 billion, which is the lowest the total has been since 2007. But despite strong market performance, by year-end that deficit had ballooned to $183 billion. 

The cause? A double whammy: a drop in interest rates that no one saw coming, and new actuarial assumptions about how long retirees might be expected to live. 

Most of the time, according to the report, actuarial losses come mostly from interest rate increases or drops. And there was definitely some of that in 2014, with the median discount used for U.S. plans falling by 0.83 percent to 4.02 percent. That meant liabilities were higher. 

But the biggest change came from the incorporation of the new mortality tables into the mix. At least 17 of the 19 club members switched to the new tables, which incorporate longer lifespans — in most cases, according to the report, the RP-2014 table that was recently published by the Society of Actuaries. That switchover boosted combined liabilities by another $29 billion. 

The previous liability high, said the report, came in 2012, when it was spurred by falling discount rates. But the 2014 total is about $23 billion higher. 

Employer contributions were also low — the lowest they’ve been since 2008 — at $16.8 billion, as employers took advantage of provisions in the Highway Transportation and Funding Act of 2014, which cut required minimum contributions that plan sponsors must pay for the next few years. 

One other factor to consider is the fact that many plan sponsors are “derisking.” While none of the club members took that route last year, “risk transfer — whether through annuity purchases or lump sums — is now an established practice among large pension plans,” said the report.