plans. Also, holding all other factors constant, an increase in the discount rate used to measure plan liabilities of 0.25 of a percentage point would decrease 2009 pension expense by approximately $30 million for U.S. pension plans and approximately $12 million for international pension plans. A decrease in the discount rate of 0.25 of a percentage point would increase 2009 pension expense by approximately $31 million for U.S. pension and plans and approximately $14 million for international pension plans. See Note 11 for details of the impact of a one percentage point change in assumed health care trend rates on the postretirement health care benefit expense and obligation.

 

Asset Impairments:

 

3M net property, plant and equipment totaled $6.9 billion as of December 31, 2008. Management makes estimates and assumptions in preparing the consolidated financial statements for which actual results will emerge over long periods of time. This includes the recoverability of long-lived assets employed in the business, including assets of acquired businesses. These estimates and assumptions are closely monitored by management and periodically adjusted as circumstances warrant. For instance, expected asset lives may be shortened or an impairment recorded based on a change in the expected use of the asset or performance of the related asset group. Impairments recorded in 2008, 2007 and 2006 related to restructuring actions and other exit activities are discussed in Note 4.

 

3M goodwill totaled approximately $5.8 billion as of December 31, 2008, which, based on impairment testing, is not impaired. Impairment testing for goodwill is done at a reporting unit level, with all goodwill assigned to a reporting unit. Reporting units are one level below the business segment level (3M has six business segments at December 31, 2008), but can be combined when reporting units within the same segment have similar economic characteristics. As of December 31, 2008, 3M did not combine any of its reporting units for impairment testing.

 

An impairment loss generally would be recognized when the carrying amount of the reporting unit’s net assets exceeds the estimated fair value of the reporting unit. The estimated fair value of a reporting unit is determined using earnings for the reporting unit multiplied by a price/earnings ratio for comparable industry groups, or by using a discounted cash flow analysis. 3M typically uses the price/earnings ratio approach for stable and growing businesses that have a long history and track record of generating positive operating income and cash flows. 3M uses the discounted cash flow approach for start-up, loss position and declining businesses, but also uses discounted cash flow as an additional tool for businesses that may be growing at a slower rate than planned due to economic or other conditions. 3M completes its annual impairment tests in the fourth quarter of each year.

 

As of December 31, 2008, 3M had 34 primary reporting units, with eight reporting units accounting for nearly 80 percent of the goodwill. At 3M, reporting units generally correspond to a division. These eight reporting units were comprised of the