Recent work indicates that the nearby Galactic halo is dominated by the debris from a major accretion event .
We confirm that result from an analysis of APOGEE-DR14 element abundances and Gaia -DR2 kinematics of halo stars .
We show that \sim 2/3 of nearby halo stars have high orbital eccentricities ( e \gtrsim 0.8 ) , and abundance patterns typical of massive Milky Way dwarf galaxy satellites today , characterised by relatively low [ Fe/H ] , [ Mg/Fe ] , [ Al/Fe ] , and [ Ni/Fe ] .
The trend followed by high e stars in the [ Mg/Fe ] - [ Fe/H ] plane shows a change of slope at [ Fe/H ] \sim - 1.3 , which is also typical of stellar populations from relatively massive dwarf galaxies .
Low e stars exhibit no such change of slope within the observed [ Fe/H ] range and show slightly higher abundances of Mg , Al and Ni .
Unlike their low e counterparts , high e stars show slightly retrograde motion , make higher vertical excursions and reach larger apocentre radii .
By comparing the position in \mathrm { [ Mg / Fe ] } - \mathrm { [ Fe / H ] } space of high e stars with those of accreted galaxies from the EAGLE suite of cosmological simulations we constrain the mass of the accreted satellite to be in the range 10 ^ { 8.5 } \lesssim M _ { * } \lesssim 10 ^ { 9 } \mathrm { M _ { \odot } } .
We show that the median orbital eccentricities of debris are largely unchanged since merger time , implying that this accretion event likely happened at z \lesssim 1.5 .
The exact nature of the low e population is unclear , but we hypothesise that it is a combination of in situ star formation , high |z| disc stars , lower mass accretion events , and contamination by the low e tail of the high e population .
Finally , our results imply that the accretion history of the Milky Way was quite unusual .