Available-for-Sale Securities (Schedule of Available-for-Sale Securities) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Jun. 30, 2017
Schedule of Available-for-sale Securities [Line Items]
Total available-for-sale securities		$ 65
Treasury bills
Schedule of Available-for-sale Securities [Line Items]
Total available-for-sale securities	$ 0	25
International bonds
Schedule of Available-for-sale Securities [Line Items]
Total available-for-sale securities	0	3
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Total available-for-sale securities	0	30
U.S. agency bonds
Schedule of Available-for-sale Securities [Line Items]
Total available-for-sale securities	0	3
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Total available-for-sale securities	0	3
International equity securities
Schedule of Available-for-sale Securities [Line Items]
Total available-for-sale securities	0	1
Recurring
Schedule of Available-for-sale Securities [Line Items]
Total available-for-sale securities	0	65
Level 2 | Recurring
Schedule of Available-for-sale Securities [Line Items]
Total available-for-sale securities	$ 0	$ 65