related expenses, including those associated with our initiatives to expand our ecosystem of digital products and services. We expect these trends to continue over time as we invest in these areas by increasing payroll and related expenses and adding technology infrastructure. 

For 2014 , 2013 , and 2012 , we capitalized $641 million (including $104 million of stock-based compensation), $581 million (including $87 million of stock-based compensation), and $454 million (including $74 million of stock-based compensation) of costs associated with internal-use software and website development. Amortization of previously capitalized amounts was $559 million , $451 million , and $327 million for 2014 , 2013 , and 2012 . A majority of our technology costs are incurred in the U.S., most of which are allocated to our North America segment. Infrastructure, other technology, and operating costs incurred to support AWS are included in technology and content. 

General and Administrative 

The increase in general and administrative costs in absolute dollars in 2014 , 2013 , and 2012 , compared to the comparable prior year periods, is primarily due to increases in payroll and related expenses and professional service fees. 

Stock-Based Compensation 

Stock-based compensation was $1.5 billion, $1.1 billion, and $833 million during 2014, 2013, and 2012. The increase in 2014, 2013, and 2012, compared to the comparable prior year periods, is primarily due to an increase in the number of stock-based compensation awards granted to existing and new employees. 

Other Operating Expense (Income)

Other operating expense (income), net was $133 million, $114 million, and $159 million during 2014, 2013, and 2012  and was primarily related to the amortization of intangible assets. 

Income from Operations 

For the reasons discussed above, income from operations decreased 76% in 2014, increased 10% in 2013 , and decreased 22% in 2012. 

Interest Income and Expense 

Our interest income was $39 million, $38 million , and $40 million during 2014 , 2013 , and 2012 . We generally invest our excess cash in investment grade short- to intermediate-term fixed income securities and AAA-rated money market funds. Our interest income corresponds with the average balance of invested funds based on the prevailing rates, which vary depending on the geographies and currencies in which they are invested. 

The primary components of our interest expense are related to our long-term debt and capital and finance lease arrangements. Interest expense was $210 million, $141 million , and $92 million in 2014 , 2013 , and 2012 . 

Our long-term debt was $8.3 billion and $3.2 billion as of December 31, 2014 and 2013. Our other long-term liabilities were $7.4 billion and $4.2 billion as of December 31, 2014 and 2013. See Item 8 of Part II, “Financial Statements and Supplementary Data—Note 6—Long-Term Debt and Note 7—Other Long-Term Liabilities” for additional information. 

Other Income (Expense)

Other income (expense), net was $(118) million, $(136) million, and $(80) million during 2014, 2013, and 2012. The primary component of other income (expense), net is related to foreign-currency