(dollars in millions) | Estimated Useful Lives | 2013 | 2012 | ||||||
Land | $ | 434 | $ | 433 | |||||
Buildings and improvements | 12-40 years | 5,633 | 5,436 | ||||||
Machinery, tools and equipment | 3-20 years | 11,353 | 10,880 | ||||||
Other, including assets under construction | 1,241 | 1,316 | |||||||
18,661 | 18,065 | ||||||||
Accumulated depreciation | (9,795 | ) | (9,547 | ) | |||||
$ | 8,866 | $ | 8,518 | ||||||