Financing Arrangement (0.75% Convertible senior notes due 2016) (Details)	1 Months Ended	12 Months Ended
	Jul. 31, 2011	Mar. 31, 2017 USD ($) shares	Mar. 31, 2016 USD ($)	Mar. 31, 2015 USD ($)	Jul. 14, 2011 USD ($) $ / shares
Financing Arrangement [Line Items]
Shares Received Under Convertible Note Hedge | shares		2,900,000
Repayments of 0.75% Convertible Senior Notes due 2016		$ 163,000,000	$ 470,000,000	$ 0
Loss on Conversion of Convertible Notes		0	$ (10,000,000)	$ 0
Convertible Debt
Financing Arrangement [Line Items]
0.75% Convertible Senior Notes due 2016, net, Principal					$ 633,000,000
Contractual interest rate of 0.75% Convertible Senior Notes due 2016					0.75%
0.75% Convertible Senior Notes due 2016, Frequency of Periodic Payment	semiannually
0.75% Convertible Senior Notes due 2016, Issuance Date	Jul. 14, 2011
Conversion rate of 0.75% Convertible Senior Notes due 2016	31.5075
0.75% Convertible Senior Notes due 2016, Face Amount					$ 1,000
Debt Instrument, Convertible, Conversion Price | $ / shares					$ 31.74
Repayments of 0.75% Convertible Senior Notes due 2016		$ 163,000,000
Debt Conversion, Converted Instrument, Shares Issued | shares		2,900,000
Debt Conversion, Converted Instrument, Amount		$ 222,000,000
Loss on Conversion of Convertible Notes		$ (300,000)