Convertible Senior Notes (Narrative) (Details) - USD ($)			3 Months Ended			12 Months Ended
		Apr. 30, 2014	Mar. 31, 2016	Mar. 31, 2015	Jun. 30, 2014	Dec. 31, 2014	Dec. 31, 2015
Debt Instrument [Line Items]
Amount used to repurchase stock			$ 28,689,000	$ 124,928,000
Convertible notes			$ 1,320,240,000				$ 1,311,071,000
Purchase From Accelerated Share Repurchase [Member]
Debt Instrument [Line Items]
Stock repurchased during period, value					$ 1,400,000,000
Senior Notes Due 2019 [Member]
Debt Instrument [Line Items]
Convertible debt						$ 1,440,000,000
Stated interest rate percentage						0.50%
Proceeds from convertible debt						$ 1,420,000,000
Payments for (proceeds from) hedge, investing activities						$ 82,600,000
Stock repurchased during period, value					1,500,000,000
Convertible debt, conversion ratio			0.0111111
Debt instrument, face amount			$ 1,000
Convertible debt, conversion price (in dollars per share)			$ 90.00
Repurchase price as a percent of principal amount			100.00%
Amortization of debt discount, effective interest method, percent			3.00%
Convertible notes			$ 1,320,240,000				1,311,071,000
Equity component	[1]		162,869,000				$ 162,869,000
Deferred tax liability, equity component			$ 8,200,000
Shares Of Common Stock Covered By Note Hedges		16,000,000
Warrant transaction		16,000,000
Class of Warrant or Right, Exercise Price of Warrants or Rights		$ 120.0
Warrants exercised (shares)			0
Privately Negotiated Transaction [Member]
Debt Instrument [Line Items]
Amount used to repurchase stock					$ 101,000,000

[1] Recorded in the condensed consolidated balance sheet within additional paid-in capital.