and our specific performance is also dependent on our and our competitors’ innovation and marketing effectiveness, and on regulatory developments affecting claims, formulations and ingredients of our products.

For all of our reporting units, there are a number of future events and factors that may impact future results and that could potentially have an impact on the outcome of subsequent goodwill impairment testing. For a list of these factors, see the “Forward-Looking Information and Factors That May Affect Future Results” section of this Financial Review and Part I. Item 1A "Risk Factors" in our 2014 Annual Report on Form 10-K.

Benefit Plans

The majority of our employees worldwide are covered by defined benefit pension plans, defined contribution plans or both. In the U.S., we have both Internal Revenue Code qualified and supplemental (non-qualified) defined benefit plans and defined contribution plans, as well as other postretirement benefit plans consisting primarily of medical insurance for retirees.

The accounting for benefit plans is highly dependent on actuarial estimates, assumptions and calculations, which can result from a complex series of judgments about future events and uncertainties. The assumptions and actuarial estimates required to estimate the employee benefit obligations for the defined benefit and postretirement plans include the discount rate; expected salary increases; certain employee-related factors, such as turnover, retirement age and mortality (life expectancy); and healthcare cost trend rates.

As of December 31, 2014, our Pension benefit obligations, net and our Postretirement benefit obligations, net increased, in the aggregate, by approximately $3.0 billion compared to December 31, 2013. The increase reflects, among other things, a decrease in our discount rate assumptions, used in the measurement of the plan obligations, as well as the impact of a change to the postretirement medical benefit plan and revised mortality assumptions (see below).

In the fourth quarter of 2014, we approved a change, effective January 1, 2016, to the postretirement medical plan to transfer certain plan participants to a retiree drug coverage program eligible for a Medicare Part D plan subsidy (Employer Group Waiver Plan). This change resulted in a decrease to the postretirement benefit obligation of approximately $600 million as of December 31, 2014.

On October 27, 2014, the Society of Actuaries (SOA) issued a new mortality table, called the SOA RP-2014 mortality table. The new SOA mortality table was created using data from 2006 and applying updated estimates of projected mortality rate improvements. The updated mortality rate projections assume that the high mortality rate improvements observed in the early 2000s will not continue, but will normalize to an ultimate improvement rate of 1.00% over a twenty-year period. In estimating our U.S. plan-specific mortality assumptions, we are using the same data and methodology used by the SOA, except that we project that the mortality rate improvements will normalize to an ultimate improvement rate of 0.75%, which is more closely aligned with the scale used by the United States