NOTE 4: GOODWILL AND OTHER INTANGIBLE ASSETS
GOODWILL. The carrying amount of goodwill and changes therein are as follows (in millions):
| Balance as of May 31, 2011 | $ | 1,085 | |||
| Goodwill acquired(1) | 104 | ||||
| Purchase adjustments and other(2) | (34) | ||||
| Balance as of May 31, 2012 | 1,155 | ||||
| Goodwill acquired(3) | 351 | ||||
| Purchase adjustments and other(2) | 20 | ||||
| Balance as of May 31, 2013(4) | $ | 1,526 | |||
| (1) | Goodwill acquired in 2012 relates to the acquisition of the Mexican domestic package delivery company, Multipak. See Note 3 for related disclosures. | ||||
| (2) | Primarily currency translation adjustments. | ||||
| (3) | Goodwill acquired in 2013 relates to the acquisitions of transportation companies in Poland, France and Brazil. See Note 3 for related disclosures. | ||||
| (4) | We do not have any accumulated impairment losses associated with our goodwill. | ||||
OTHER INTANGIBLE ASSETS. The net book value of our other intangible assets was $63 million at May 31, 2013 and $19 million at May 31, 2012. Amortization expense for intangible assets was $22 million in 2013, $11 million in 2012 and $4 million in 2011. Estimated amortization expense is expected to be immaterial in 2014 and beyond.