Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
|  |  |  | Year Ended December 31, | Year Ended December 31, | Year Ended December 31, |
| --- | --- | --- | --- | --- | --- |
|  |  |  | 2017 | 2016 | 2015 |
| (In millions) | Total operating expenses – GAAP |  | $38,149 | $34,896 | $34,786 |
| Less regional expenses: | (In millions) | Fuel and related taxes | (1,382) | (1,109) | (1,230) |
| Less regional expenses: | (In millions) | Other | (5,164) | (4,935) | (4,753) |
| Less regional expenses: | (In millions) | Total mainline operating expenses | 31,603 | 28,852 | 28,803 |
| Less regional expenses: | (In millions) | Adjusted for: Special items, net (1) | (712) | (709) | (1,051) |
| Less regional expenses: | (In millions) | Adjusted for: Aircraft fuel and related taxes | (6,128) | (5,071) | (6,226) |
| Less regional expenses: | (In millions) | Mainline operating expenses excluding special items and fuel | $24,763 | $23,072 | $21,526 |
| (In millions) | Available Seat Miles (ASM) |  | 243,806 | 241,734 | 239,375 |
| (In cents) | Mainline CASM |  | 12.96 | 11.94 | 12.03 |
| (In cents) | Adjusted for: Special items, net per ASM |  | (0.29) | (0.29) | (0.44) |
| (In cents) | Adjusted for: Aircraft fuel and related taxes per ASM |  | (2.51) | (2.10) | (2.60) |
| (In cents) | Mainline CASM excluding special items and fuel |  | 10.16 | 9.54 | 8.99 |
Question:
What were American airlines' total operating expenses or GAAP by the end of 2015?
Answer:
$34,786