DEBT (Narrative) (Details) - USD ($)		1 Months Ended			3 Months Ended		12 Months Ended
	Aug. 20, 2014	May. 31, 2013	Mar. 31, 2012	Oct. 31, 2011	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jun. 30, 2013	Mar. 31, 2010
Debt Instrument
Long-term Debt					$ 5,304,108,000		$ 3,849,756,000
Letters of credit issued					3,900,000		4,000,000
Estimated market value of outstanding debt					6,200,000,000		4,800,000,000
Description of Senior Notes
Unamortized debt discount					344,350,000		360,312,000
Amortization of debt discount included in interest expense					16,691,000	$ 12,412,000
Gains (Losses) on Extinguishment of Debt					(3,000)	(3,396,000)
Convertible Notes [Member]
Description of Senior Notes
Interest expense related to convertible notes					23,300,000	17,100,000
Contractual coupon interest related to convertible notes included in interest expense					5,700,000	3,500,000
Amortization of debt discount included in interest expense					16,500,000	12,400,000
Amortization of debt issuance costs					1,100,000	1,200,000
Gains (Losses) on Extinguishment of Debt						(3,400,000)
Extinguishment of Debt, Gain (Loss), Net of Tax						(2,100,000)
1.25% Convertible Senior Notes due March 2015 [Member]
Debt Instrument
Reclassification of Unamortized Debt Discount							$ 300,000
Description of Senior Notes
Aggregate Principal Amount											$ 575,000,000
Interest rate on Long-term Debt							1.25%				1.25%
Convertible debt conversion price (in dollars per share)											$ 303.06
Unamortized debt discount							$ 329,000
Debt Conversion Cash Delivered for Principal Due on Converted Debt					37,500,000
Debt Conversion, Converted Instrument, Shares Issued					110,100,000
Debt discount related to convertible notes, net of tax											$ 69,100,000
Debt discount related to convertible notes, before tax											115,200,000
Debt Instrument, Convertible Carrying Amount Of The Equity Component Related To Finance Costs Net Of Tax											$ 1,600,000
1.00% Convertible Senior Notes Due March 2018 [Member]
Debt Instrument
Long-term Debt					$ 930,778,000		$ 925,166,000
Description of Senior Notes
Aggregate Principal Amount			$ 1,000,000,000
Interest rate on Long-term Debt			1.00%		1.00%		1.00%
Debt financing costs paid									$ 20,900,000
Convertible debt conversion price (in dollars per share)			$ 944.61
Ratio of closing share price to conversion price as a condition for conversion of convertible 2015 Senior Notes, minimum			150.00%
Unamortized debt discount					$ 69,222,000		$ 74,834,000
Effective interest rate at debt origination or modification			3.50%
Debt discount related to convertible notes, net of tax			$ 80,900,000
Debt discount related to convertible notes, before tax			135,200,000
Debt Instrument, Convertible Carrying Amount Of The Equity Component Related To Finance Costs Net Of Tax			$ 2,800,000
0.35 % Convertible Senior Notes Due June 2020 [Member]
Debt Instrument
Long-term Debt					$ 867,760,000		$ 861,886,000
Description of Senior Notes
Aggregate Principal Amount		$ 1,000,000,000
Interest rate on Long-term Debt		0.35%			0.35%		0.35%
Debt financing costs paid								$ 1,000,000
Convertible debt conversion price (in dollars per share)		$ 1,315.10
Ratio of closing share price to conversion price as a condition for conversion of convertible 2015 Senior Notes, minimum		150.00%
Unamortized debt discount		$ 20,000,000			$ 132,240,000		$ 138,114,000
Effective interest rate at debt origination or modification		3.13%
Debt discount related to convertible notes, net of tax										$ 92,400,000
Debt discount related to convertible notes, before tax										154,300,000
Debt Instrument, Convertible Carrying Amount Of The Equity Component Related To Finance Costs Net Of Tax										$ 100,000
Amortization of debt discount included in interest expense					700,000	$ 700,000
0.9% Convertible Senior Notes Due September 2021 [Member]
Debt Instrument
Long-term Debt					$ 868,338,000		$ 863,701,000
Description of Senior Notes
Aggregate Principal Amount	$ 1,000,000,000
Interest rate on Long-term Debt	0.90%				0.90%		0.90%
Debt financing costs paid							$ 11,000,000
Convertible debt conversion price (in dollars per share)	$ 2,055.50
Ratio of closing share price to conversion price as a condition for conversion of convertible 2015 Senior Notes, minimum	150.00%
Unamortized debt discount					$ 131,662,000		136,299,000
Effective interest rate at debt origination or modification	3.18%
Debt discount related to convertible notes, net of tax							82,500,000
Debt discount related to convertible notes, before tax							142,900,000
Debt Instrument, Convertible Carrying Amount Of The Equity Component Related To Finance Costs Net Of Tax							1,600,000
Convertible Debt Liability [Member]
Description of Senior Notes
Debt, Weighted Average Interest Rate					3.50%	3.60%
Minimum [Member] | 1.00% Convertible Senior Notes Due March 2018 [Member]
Description of Senior Notes
Minimum and Maximum consecutive days the closing sales price of common stock must exceed a specified percentage of conversion price to trigger conversion feature of note (in days)			20 days
Additional Payment To Debt Holder Settled In Shares Aggregate Value Of Shares			$ 0
Minimum [Member] | 0.35 % Convertible Senior Notes Due June 2020 [Member]
Description of Senior Notes
Minimum and Maximum consecutive days the closing sales price of common stock must exceed a specified percentage of conversion price to trigger conversion feature of note (in days)		20 days
Additional Payment To Debt Holder Settled In Shares Aggregate Value Of Shares		$ 0
Minimum [Member] | 0.9% Convertible Senior Notes Due September 2021 [Member]
Description of Senior Notes
Minimum and Maximum consecutive days the closing sales price of common stock must exceed a specified percentage of conversion price to trigger conversion feature of note (in days)	20 days
Additional Payment To Debt Holder Settled In Shares Aggregate Value Of Shares	$ 0
Maximum [Member] | 1.00% Convertible Senior Notes Due March 2018 [Member]
Description of Senior Notes
Minimum and Maximum consecutive days the closing sales price of common stock must exceed a specified percentage of conversion price to trigger conversion feature of note (in days)			30 days
Additional Payment To Debt Holder Settled In Shares Aggregate Value Of Shares			$ 344,000,000
Maximum [Member] | 0.35 % Convertible Senior Notes Due June 2020 [Member]
Description of Senior Notes
Minimum and Maximum consecutive days the closing sales price of common stock must exceed a specified percentage of conversion price to trigger conversion feature of note (in days)		30 days
Additional Payment To Debt Holder Settled In Shares Aggregate Value Of Shares		$ 397,000,000
Maximum [Member] | 0.9% Convertible Senior Notes Due September 2021 [Member]
Description of Senior Notes
Minimum and Maximum consecutive days the closing sales price of common stock must exceed a specified percentage of conversion price to trigger conversion feature of note (in days)	30 days
Additional Payment To Debt Holder Settled In Shares Aggregate Value Of Shares	$ 375,000,000
Convertible Debt Converted Debt [Member]
Description of Senior Notes
Charge off of deferred debt issuance cost						$ 300,000
Revolving Credit Facility [Member]
Debt Instrument
Revolving credit facility, maximum borrowing capacity				$ 1,000,000,000.0
Period of revolving credit facility (in years)				5 years
Long-term Debt					$ 0		$ 0
Revolving Credit Facility [Member] | Minimum [Member]
Debt Instrument
Commitment fee rate				0.10%
Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument
Commitment fee rate				0.25%
Letter of Credit [Member]
Debt Instrument
Revolving credit facility, maximum borrowing capacity				$ 100,000,000.0
Swingline Loans [Member]
Debt Instrument
Revolving credit facility, maximum borrowing capacity				$ 50,000,000.0
Rate 2C [Member] | Revolving Credit Facility [Member] | Minimum [Member]
Debt Instrument
Basis spread on variable rate				0.00%
Rate 2C [Member] | Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument
Basis spread on variable rate				0.50%
London Interbank Offered Rate (LIBOR) [Member] | Rate 1 [Member] | Revolving Credit Facility [Member] | Minimum [Member]
Debt Instrument
Basis spread on variable rate				1.00%
London Interbank Offered Rate (LIBOR) [Member] | Rate 1 [Member] | Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument
Basis spread on variable rate				1.50%
Federal funds rate [Member] | Rate 2B [Member] | Revolving Credit Facility [Member]
Debt Instrument
Basis spread on variable rate				0.50%
One month LIBOR [Member] | Rate 2C [Member] | Revolving Credit Facility [Member]
Debt Instrument
Basis spread on variable rate				1.00%