Primary Biliary Cholangitis (PBC): This condition is characterized by chronic inflammation and destruction of the bile ducts within the liver, leading to cholestasis. The presentation of generalized pruritus, elevated alkaline phosphatase (alk phos), and transaminitis, along with common duct dilatation without obstruction, is consistent with PBC. The age and potential female predominance (though it can occur in males) also align with this diagnosis.

Primary Sclerosing Cholangitis (PSC): Although more commonly associated with inflammatory bowel disease and often presenting at a younger age, PSC can cause similar laboratory and clinical findings, including pruritus and elevated liver enzymes. The common duct dilatation could be due to sclerosing cholangitis.
Cholestasis due to Drug-Induced Liver Injury: Certain medications can cause cholestatic liver injury, leading to elevated alk phos, transaminitis, and pruritus. The absence of obstruction and the presence of common duct dilatation might be seen in this context, depending on the drug and the individual's response.
Hepatocellular Carcinoma with Bile Duct Invasion: Although less common, a tumor could cause both obstructive and non-obstructive jaundice and pruritus, especially if it invades the bile ducts. The elevated liver enzymes and alk phos would support this diagnosis.

Pancreatic Cancer: This is a critical diagnosis not to miss, as it can present with painless jaundice, pruritus (due to bile duct obstruction), and elevated liver enzymes. The common duct dilatation without obvious obstruction could be due to a tumor at the ampulla of Vater or pancreatic head.
Cholangiocarcinoma: Similar to pancreatic cancer, cholangiocarcinoma can cause obstructive jaundice, pruritus, and elevated liver enzymes. It's essential to consider this diagnosis, especially given the common duct dilatation.

Sarcoidosis Involving the Liver and Bile Ducts: Sarcoidosis can cause granulomatous inflammation in the liver, leading to cholestasis, elevated alk phos, and pruritus. Although rare, it's a consideration in patients with unexplained liver enzyme elevations and systemic symptoms.
Lymphoma Involving the Liver and Bile Ducts: Certain types of lymphoma can infiltrate the liver and cause cholestasis, leading to pruritus and elevated liver enzymes. This diagnosis would be rare but should be considered in the differential, especially if other systemic symptoms or lymphadenopathy are present.