Umeclidinium/vilanterol (UMEC/VI) is a combination product under development that is used for the treatment of airflow obstruction in patients with COPD. Fluticasone propionate/salmeterol (FSC) is an approved drug that is already in use for the treatment of COPD. This is a multicenter, randomized, double-blind, double-dummy, parallel group study to evaluate the efficacy and safety of UMEC/VI 62.5/25 microgram [mcg] once daily administered via Novel Dry Powder Inhaler (NDPI) compared with fluticasone propionate /salmeterol (FSC) 250/50 mcg twice-daily when administered via ACCUHALER/DISKUS inhaler over a treatment period of 12 weeks in subjects with COPD. Eligible subjects will be equally randomized to UMEC/VI 62.5/25 mcg or FSC 250/50 mcg for 12 weeks. A safety follow-up assessment will be conducted approximately 7 days after the end of the study treatment.