The leptonic and inclusive hadronic decay branching fractions of the W boson are measured using proton-proton collision data collected at √s = 13 TeV by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of 35.9 fb^-1. Events characterized by the production of one or two W bosons are selected and categorized based on the multiplicity and flavor of reconstructed leptons, the number of jets, and the number of jets identified as originating from the hadronization of b quarks. A binned maximum likelihood estimate of the W boson branching fractions is performed simultaneously in each event category. The measured branching fractions of the W boson decaying into electron, muon, and tau lepton final states are (10.83 ± 0.10)%, (10.94 ± 0.08)%, and (10.77 ± 0.21)%, respectively, consistent with lepton flavor universality for the weak interaction. The average leptonic and inclusive hadronic decay branching fractions are estimated to be (10.89 ± 0.08)% and (67.32 ± 0.23)%, respectively. Based on the hadronic branching fraction, three standard model quantities are subsequently derived: the sum of squared elements in the first two rows of the Cabibbo-Kobayashi-Maskawa (CKM) matrix ∑_ij|V_ij|² = 1.984 ± 0.021, the CKM element |V_cs| = 0.967 ± 0.011, and the strong coupling constant at the W boson mass scale, α_S(m²_W) = 0.095 ± 0.033.