Reportable Segments - Total Assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Sep. 30, 2018
Segment Reporting Information [Line Items]
Total assets	$ 22,744	$ 23,783
Media Networks
Segment Reporting Information [Line Items]
Total assets	17,464	17,576
Filmed Entertainment
Segment Reporting Information [Line Items]
Total assets	5,427	5,297
Corporate/Eliminations
Segment Reporting Information [Line Items]
Total assets	$ (147)	$ 910