Fair Value Measurements (Tables)

12 Months Ended

Mar. 31, 2018

Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]

Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation

Assets measured at fair value on a recurring basis at March 31, 2018 are as follows (amounts in millions):

	Quoted Prices in Active Markets for  Identical Instruments (Level 1)		Significant Other Observable Inputs (Level 2)		Total Balance
Assets
Cash and cash equivalents:
Money market mutual funds	$	121.0	$	—	$	121.0
Deposit accounts	—		641.6		641.6
Commercial Paper	—		118.7		118.7
Government agency bonds	—		20.0		20.0
Short-term investments:
Marketable equity securities	2.8		—		2.8
Corporate bonds and debt	—		542.9		542.9
Time deposits	—		11.5		11.5
Government agency bonds	—		723.2		723.2
Municipal bonds - taxable	—		14.9		14.9
Total assets measured at fair value	$	123.8	$	2,072.8	$	2,196.6

Assets measured at fair value on a recurring basis at March 31, 2017 are as follows (amounts in millions):

	Quoted Prices in Active Markets for  Identical Instruments (Level 1)		Significant Other Observable Inputs (Level 2)		Total Balance
Assets
Cash and cash equivalents:
Money market mutual funds	$	343.8	$	—	$	343.8
Deposit accounts	—		564.9		564.9
Short-term investments:
Marketable equity securities	1.6		—		1.6
Corporate bonds and debt	—		165.2		165.2
Government agency bonds	—		162.0		162.0
Municipal bonds - tax-exempt	—		55.3		55.3
Municipal bonds - taxable	—		10.0		10.0
Long-term Investments:
Corporate bonds and debt	—		42.6		42.6
Government agency bonds	—		64.9		64.9
Total assets measured at fair value	$	345.4	$	1,064.9	$	1,410.3