Financial Instruments (Summary of Estimated Fair Value of Long-term Obligations and Other Short-term Borrowings) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Jun. 30, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying amount	$ 9,001	$ 9,013
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value	$ 8,858	$ 8,852