Marketable Investment Securities - Schedule of Fair Value for Available-for-Sale Securities by Major Security Type and Class of Security (Detail) - USD ($) $ in Millions	Jun. 30, 2015	Jun. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 185.4	$ 270.2
Gross unrealized holding gains	0.1	0.3
Gross unrealized holding losses	(0.1)
Estimated fair value	185.4	270.5
Cash
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	54.7	45.2
Estimated fair value	54.7	45.2
Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	9.4	19.6
Estimated fair value	9.4	19.6
Total Cash and Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	64.1	64.8
Estimated fair value	64.1	64.8
Corporate Bonds and Notes
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	41.8	44.5
Estimated fair value	41.8	44.5
Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	66.3	137.8
Gross unrealized holding gains	0.1	0.3
Gross unrealized holding losses	(0.1)
Estimated fair value	66.3	138.1
Federal Agency Issues
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	13.2	23.1
Estimated fair value	$ 13.2	$ 23.1