Comparison of NN5401 With Insulin Glargine, Both in Combination With Oral Antidiabetic Drugs, in Subjects With Type 2 Diabetes

Inclusion Criteria: * Type 2 diabetes mellitus (diagnosed clinically) for at least 6 months * Treatment with basal insulin regimen (insulin detemir, insulin glargine or neutral protamine Hagedorn \[NPH\] insulin) once daily (OD), for at least 3 months * Ongoing treatment with: metformin with or without other oral antidiabetic drugs (OADs) for at least 3 months prior to randomisation * HbA1c 7.0-10.0 % (both inclusive) by central laboratory analysis * BMI maximum 40.0 kg/m\^2 Exclusion Criteria: * Treatment with insulin regimens other than a basal insulin regimen (insulin detemir or insulin glargine or NPH insulin) OD within 3 months prior to Visit 1 * Treatment with glucagon-like peptide 1 (GLP-1) receptor agonists within 3 months prior to visit 1 * Current rosiglitazone users * Cardiovascular disease, within the last 6 months prior to visit 1, defined as: stroke; decompensated heart failure New York Heart Association (NYHA) class III or IV; myocardial infarction; unstable angina pectoris; or coronary arterial bypass graft or angioplasty * Uncontrolled treated/untreated severe hypertension (systolic blood pressure at least 180 millimetre (mm) mercury (Hg) and/or diastolic blood pressure at least 100 mmHg) * Impaired liver function, defined as alanine aminotransferase (ALAT) at least 2.5 times upper limit of normal (one retest analysed at the central laboratory within a week of receipt of the result is permitted with the result of the last sample being conclusive) * Pregnancy, breast-feeding, the intention of becoming pregnant or not using adequate contraceptive measures according to local requirements * Cancer and medical history of cancer hereof (except basal cell skin cancer or squamous cell skin cancer)