We present a measurement of the ratio of top quark branching fractions $R=\mathcal{B}(t\ensuremath{\rightarrow}Wb)/\mathcal{B}(t\ensuremath{\rightarrow}Wq)$, where $q$ can be a $d$, $s$, or $b$ quark, in the $\mathrm{\text{lepton}}+\mathrm{\text{jets}}$ and dilepton $t\overline{t}$ final states. The measurement uses data from $5.4\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of $p\overline{p}$ collisions collected with the D0 detector at the Fermilab Tevatron Collider. We measure $R=0.90\ifmmode\pm\else\textpm\fi{}0.04$, and we extract the Cabibbo-Kobayashi-Maskawa (CKM) matrix element $|{V}_{\mathrm{tb}}|$ as $|{V}_{\mathrm{tb}}|=0.95\ifmmode\pm\else\textpm\fi{}0.02$, assuming unitarity of the $3\ifmmode\times\else\texttimes\fi{}3$ CKM matrix.