Heavy disinformation going around that this exempts American citizens. Not true, though it is cleverly-written. In addition to Sen. Lindsey Graham saying point blank that it does include American citizens, Senior Legislative Counsel for Washington ACLU, Chris Anders, explains:
Don’t be confused by anyone claiming that the indefinite detention legislation does not apply to American citizens. It does. There is an exemption for American citizens from the mandatory detention requirement (section 1032 of the bill), but no exemption for American citizens from the authorization to use the military to indefinitely detain people without charge or trial (section 1013 of the bill). So, the result is that, under the bill, the military has the power to indefinitely imprison American citizens,
Vote on full bill tomorrow, Wednesday November 30. Lindsey Graham (R-SC) transcript and CSPAN speech:

[b]"1031, the statement of authority to detain, does apply to American citizens and it designates the world as the battlefield, including the homeland.â€