Commitments and Contingencies (Details) ft² in Thousands, $ in Millions		3 Months Ended		9 Months Ended
	Jul. 10, 2015 USD ($) ft²	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Mar. 31, 2014 USD ($)	Mar. 31, 2011 USD ($)
Summarization of principal contractual obligations
Future minimum payments under the non-cancelable operating leases	$ 118.1	$ 123.1		$ 123.1
Rent expense		33.2	$ 36.5	10.8	$ 10.8
Lease term, option to extend	20 years
Square feet of leased space | ft²	63
Term of lease	10 years
Tenant allowance	$ 6.0
Property and equipment, net		959.9		959.9			$ 904.3
Total purchase commitments		558.7		558.7
Accrual for estimated carrying charges or obsolete materials charges		19.2		19.2
Short-term debt		299.9		299.9			0.0
Long-term debt, carrying value		1,648.7		1,648.7			1,349.0
Indemnity-related and service-related escrows		33.9		33.9
Campus build out commitments		3.5		3.5
Other contractual obligations		22.5		22.5
Long-term income taxes payable		185.0		185.0			$ 177.5
Construction in Progress [Member]
Summarization of principal contractual obligations
Property and equipment, net		10.1		10.1
Fixed rate note due 2016 [Member]
Summarization of principal contractual obligations
Short-term debt, gross		$ 300.0		$ 300.0					$ 300.0
Short-term and Long-term debt, stated interest rate		3.10%		3.10%					3.10%
Fixed rate note due 2020 [Member]
Summarization of principal contractual obligations
Long-term debt, gross		$ 300.0		$ 300.0		$ 300.0
Short-term and Long-term debt, stated interest rate		3.30%		3.30%		3.30%
Fixed rate note due 2021 [Member]
Summarization of principal contractual obligations
Long-term debt, gross		$ 300.0		$ 300.0					$ 300.0
Short-term and Long-term debt, stated interest rate		4.60%		4.60%					4.60%
Fixed rate note due 2024 [Member]
Summarization of principal contractual obligations
Long-term debt, gross		$ 350.0		$ 350.0				$ 350.0
Short-term and Long-term debt, stated interest rate		4.50%		4.50%				4.50%
Fixed rate note due 2025 [Member]
Summarization of principal contractual obligations
Long-term debt, gross		$ 300.0		$ 300.0		$ 300.0
Short-term and Long-term debt, stated interest rate		4.35%		4.35%		4.35%
Fixed rate note due 2041 [Member]
Summarization of principal contractual obligations
Long-term debt, gross		$ 400.0		$ 400.0					$ 400.0
Short-term and Long-term debt, stated interest rate		5.95%		5.95%					5.95%
Minimum [Member]
Summarization of principal contractual obligations
Increment for lease extension	5 years
Maximum [Member]
Summarization of principal contractual obligations
Increment for lease extension	10 years