Bottom Line: Learn two quick ways to remove the indentation on multiple cells when the indentation is set at different levels.
Skill Level: Beginner
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Follow along using the same file I use in the video.
Removing Indentation from Multiple Cells
Sometimes the formatting of a sheet has indentation on multiple levels, such as with this example of an income statement.

Removing all of the indentations can be a time-consuming task. If you select all of the cells that contain indentation (at multiple levels) and press the Decrease Indent button, nothing happens. The indentation is NOT removed.

Fortunately, there are ways to quickly remove the indentation at multiple levels all at one time. Let's take a look at two techniques.
1. Change Alignment to General
The first way to take care of this issue is to change the alignment of the cells to the General setting.
Start by selecting all of the cells that you want to remove the indentation for. Then click the Left Align button to change the alignment to General.

The indentation will be removed. The values in the cells will use the General Alignment, which differs based on the data type of the cell. Text will be aligned to the left. Numbers and dates aligned to the right.

Note: If the Left Align button is not already enabled, or you have different alignment settings for each cell, then you will have to press the Left Align button twice to change the alignment to General.
2. Remove Indenation but Keep Alignment Settings
There may be cases where you have cells in your selection that you don't want to clear the alignment for. Perhaps you have some merged cells, or text that is center-aligned, or some that are right-aligned, such as in this example.

If that's the case, you can use this second technique. Start by selecting the range of cells that you want to work with. The selection can include cells that are not indented and have other alignment settings applied.
Then right-click and choose Format Cells. The keyboard shortcut for this is Ctrl + 1.

When the Format Cells window opens, go to the Alignment tab and set the Indent field to 0.

As you can see below, the result is that the alignment remains the same, but the indentation goes away.

Conclusion
Pretty easy, huh? I hope these techniques help save you time over having to clear indentation one by one. If you have any questions or suggestions, I invite you to leave a comment below.
If the text in the cell is set to the currency or comma format, that wouldn’t that also be a reason that the text in all the cells are not in complete alignment?
Meaning, even after doing what you suggested, of going onto the alignment and setting it to 0, (which, btw, is a great tip…I never thought of it), if the cell is set to comma or currency, I don’t believe it will fix the issue, which can be extremely frustrating.
You can, by the way, set the formatting to line up the decimal points in a column.
You use a custom format like: “#.???” with enough “?” characters after the decimal point to account for as many decimal places as you care to have, within Excel’s limits for such.
Use too few and like usual, Excel will display a rounded value for longer entries and the decimal points will still all line up.