Colocation Business, of the \$91 million increase in depreciation expense on these real estate assets, \$44 million is not expected to recur in future periods.

Amortization expense increased by \$1 million, or less than 1%, for the year ended December 31, 2017 as compared to the year ended December 31, 2016 and decreased by \$128 million, or 9%, for the year ended December 31, 2016 as compared to the year ended December 31, 2015. The increase in amortization expense for the year ended December 31, 2017 was primarily attributable to the inclusion of \$139 million in post-acquisition Legacy Level 3 amortization expense in our consolidated amortization expense. Legacy CenturyLink’s amortization expense was lower for both periods primarily due to the use of accelerated amortization for a portion of our customer relationship assets and our entry into an agreement to sell our data centers and colocation business. The effect of using an accelerated amortization method results in an incremental decline in expense each period as the intangible assets amortize. We ceased amortizing the intangible assets of our colocation business when we entered into the agreement to sell that business. Absent the sale, we estimate that we would have recorded additional amortization expense of \$13 million from January 1, 2017 through May 1, 2017, related to the conveyed intangible assets. In addition, amortization of capitalized software was lower in both periods due to software becoming fully amortized faster than new software was acquired or developed.

# Other Consolidated Results

The following tables summarize our total other expense, net and income tax (benefit) expense:

Years Ended
December 31,	Increase/
(Decrease)	%
Change
2017	2016
(Dollars in millions)
Interest expense ..............................................	$(1,481)	(1,318)	163	12 %
Other income, net . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	12	5	7	140 %
Total other expense, net ........................................	$(1,469)	(1,313)	156	12 %
Income tax (benefit) expense ....................................	$ (849)	394	(1,243)	nm

Years Ended
December 31,	Increase/
(Decrease)	%
Change
2016	2015
(Dollars in millions)
Interest expense ..............................................	$(1,318)	(1,312)	6	— %
Other income, net . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	5	49	(44)	(90)%
Total other expense, net ........................................	$(1,313)	(1,263)	50	4 %
Income tax expense . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	$ 394	438	(44)	(10)%

nm - Percentages greater than 200% and comparisons between positive and negative values or to/from zero values are considered not meaningful.

# Interest Expense

Interest expense increased by \$163 million, or 12%, for the year ended December 31, 2017 as compared to the year ended December 31, 2016. The increase in interest expense was primarily due to (i) the issuance of\$7.945 billion of term loans in 2017 for the purpose of providing funding for the Level 3 acquisition, (ii) the assumption of Level 3’s debt upon the consummation of the acquisition of Level 3, which accounted for\$80 million in post-acquisition interest expense and (iii) the recognition of imputed interest expense resulting from the failed-sale-leaseback as further described in Note 3—Sale of Data Centers and Colocation Business. Interest expense increased by \$6 million, or less than 1%, for the year ended December 31, 2016 as compared to the year ended December 31, 2015. The increase in interest expense was substantially due to a reduction in the