A 2-way splitter can be used that way, provided that there are NO other splitters between the pole drop feeding your home and the specific wall outlet. Any other splitter brings extra signal loss to all connected devices. If there is another splitter, you can bypass it using an F-junction to join the pole drop cable to the cable directly feeding the wall outlet.
Also be sure that both of the short jumpers to your TV and modem are made with real RG-6 cable, as marked on the jacket. Don't use the cheaper RG-59 type that used to be supplied with analog VCRs and cable boxes.
To refine this response, splitters can be used as long as:
1. Doesn't exceed maxium Tx/Return/Upstream RF power level
(effectively need to keep less than or equal to 50 dBmV)
2. Does't exceed minimum effective Rx/Forward/Downstream RF power level
(effectively need to keep more than to -8 dBmV)
3. Is shielded at at least 110 dB and any fittings attached are quality compression fittings (no hex crimp, no twist on) and tightened down to 20 inch/lbs torque (slightly more than finger-tight).
Antronix, ChannelPlus, and Extreme all make various 1GHz-rated splitters (and amps) that will work. Don't use the "golden" crap splitters with paper-thin metal back plates and barely any sodering used to seal them up. The fittings typically used by in-house Charter/Spectrum techs are the PPC EX6PLUS. I've seen DirectTV and ComCast use those PPC fittings too, but usually the EX6XLWSPLUS or EX6XL versions, they seem to be popular and hold up well to outside weather.