A Trial Comparing the Efficacy and Safety of Insulin Degludec and Insulin Glargine 300 Units/mL in Subjects With Type 2 Diabetes Mellitus Inadequately Treated With Basal Insulin With or Without Oral Antidiabetic Drugs

Inclusion criteria: - Male or female, age above or equal to 18 years at the time of signing informed consent. - Subjects fulfilling at least one of the below criteria (For this inclusion criterion the aim is to include minimum 80% of individuals with a previous episode of hypoglycaemia (criterion e). The remaining subjects will have to fulfil at least one of criteria a-d.): - a) Experienced at least one severe hypoglycaemic episode within the last year (according to the ADA definition, April 2013 (An episode requiring assistance of another person to actively administer carbohydrate, glucagon, or take other corrective actions. Plasma glucose concentrations may not be available during an event, but neurological recovery following the return of plasma glucose to normal is considered sufficient evidence that the event was induced by a low plasma glucose concentration.). - b) Moderate chronic renal failure, defined as glomerular filtration rate 30 - 59 mL/min/1.73 m\^2 per CKD-EPI by central laboratory analysis. - c) Hypoglycaemic symptom unawareness (History of impaired autonomic responses (tremulousness, sweating, palpitations, and hunger) during hypoglycaemia). - d) Treated with insulin for more than 5 years. - e) Episode of hypoglycaemia (defined by symptoms of hypoglycaemia and/or episode with low glucose measurement (equal to or below 70 mg/dL \[equal to or below 3.9 mmol/L\])) within the last 12 weeks prior to Visit 1 (screening). - Subjects diagnosed (clinically) with type 2 diabetes mellitus. - Treated with basal only insulin (once daily or twice-daily insulin (insulin detemir; insulin glargine 100 U/mL, biosimilar of insulin glargine 100 U/mL or insulin Neutral Protamine Hagedorn)) equal to or above 90 days prior to the day of screening with or without any of the following anti-diabetic drugs with stable doses for equal to or above 90 days prior to screening: - a) Metformin - b) Dipeptidyl peptidase -4 inhibitor - c) Sodium-glucose co-transporter 2 inhibitor - d) Alpha-glucosidase-inhibitors (acarbose) - e) Thiazolidinediones - f) Marketed oral combination products only including the products listed in criteria 5a-5e - HbA1c equal to or below 9.5% (80 mmol/mol) at screening by central laboratory analysis. - BMI equal to or below 45 kg/m\^2. Exclusion Criteria: - Treatment with any medication for the indication of diabetes or obesity other than stated in the inclusion criteria in a period of 90 days before the day of screening