Valuations utilize significant unobservable inputs (level 3) when determining the fair value of energy assets. The significant level  3 inputs include:  Valuation technique(s) Significant unobservable input(s) Relationship of unobservable input(s) to fair value Discounted cash flow models • Future cash flows – primarily  driven by transmission, distribution  and storage volumes and pricing • Increases (decreases) in future cash flows will  increase (decrease) the fair value • Discount rate • Increases (decreases) in discount rate will decrease  (increase) the fair value • Terminal capitalization  multiple • Increases (decreases) in terminal capitalization  multiple will decrease (increase) the fair value • Investment Horizon • Increases (decreases) in the investment horizon will  decrease (increase) the fair value YEARS ENDED DECEMBER 31  (MILLIONS) 2013 2012 Balance at beginning of year  $ 833 $ 118 Additions, net of disposals  33 17 Acquisitions through business combinations  142 685 Foreign currency translation  (47) 13 Balance at end of year  $ 961 $ 833 YEARS ENDED DECEMBER 31  (MILLIONS) 2013 2012 Balance at beginning of year  $ 33 $ — Fair value changes  83 33 Foreign currency translation  1 — Balance at end of year  $ 117 $ 33 YEARS ENDED DECEMBER 31  (MILLIONS) 2013 2012 Balance at beginning of year  $ (9) $ — Depreciation expense  (37) (9) Foreign currency translation  (3) — Balance at end of year  $ (49) $ (9) (MILLIONS) 2013 2012 Cost  $ 666 $ 1,461 Accumulated fair value changes  165 (18) Accumulated depreciation  (30) (31) Total  $ 801 $ 1,412 Property, plant and equipment within our sustainable resources operations are accounted for under the revaluation model and the  most recent date of revaluation was December 31, 2013. iv.  Infrastructure – Sustainable Resources Sustainable resources assets represents timberlands and other agricultural land. The following table presents the changes to the accumulated depreciation of the company’s transport and energy assets: The following table presents the changes to the cost of the company’s energy assets: The following table presents the changes to the accumulated fair value changes of the company’s transport and energy assets: Key assumptions used in the December 31, 2013 valuation process include: discount rates ranging from 15% to 16%  (2012 – 12% to 15%), terminal capitalization multiples ranging from 8x to 12x (2012 – 7x to 8x), and an investment horizon of  10 years (2012 – 10 years). 2013 ANNUAL REPORT 121