Fair Value Measurements (Details) - USD ($) $ in Millions	Dec. 31, 2018	Sep. 30, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-Marketable Securities	$ 89
Notional value of foreign currency contracts	670	$ 642
Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable Securities, Noncurrent	34	80
Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative, Fair Value, Net	(11)	(8)
Net Investments In Foreign Operations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional value of foreign currency contracts	215	297
Future Production Costs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional value of foreign currency contracts	455	345
Senior Notes and Senior and Junior Debentures [Member] | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Fair Value Disclosure	$ 8,900	$ 10,500