CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)		12 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net income		$ 355,900,000	$ 255,400,000	$ 164,600,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		876,400,000	615,900,000	469,200,000
Deferred income taxes		(62,200,000)	51,200,000	(126,900,000)
Share-based compensation expense related to equity incentive plans		166,400,000	93,200,000	128,100,000
Loss on settlement of debt		12,600,000	16,000,000.0	43,900,000
Amortization of debt discount		114,600,000	106,100,000	56,100,000
Amortization of debt issuance costs		16,500,000	6,600,000	4,500,000
Losses on equity method investments		200,000	200,000	200,000
Gains on sale of assets		0	(5,900,000)	(100,000)
Losses on write-down of fixed assets		800,000	100,000	2,600,000
Impairment of intangible assets		3,100,000	500,000	11,900,000
Losses on available-for-sale investments and marketable equity securities, net		0	0	100,000
Realized gain on equity method investment		0	0	(400,000)
Impairment of available-for-sale investment		6,000,000.0	15,500,000	1,400,000
Amortization of premium on available-for-sale investments		(200,000)	300,000	0
Changes in operating assets and liabilities, excluding impact of acquisitions:
Decrease (increase) in accounts receivable		238,800,000	(85,300,000)	(46,800,000)
Decrease (increase) in inventories		341,600,000	(59,200,000)	223,700,000
Increase in deferred income on shipments to distributors		0	41,000,000.0	109,400,000
Decrease in accounts payable and accrued liabilities		(180,700,000)	(13,900,000)	(14,800,000)
Change in other assets and liabilities		(24,200,000)	14,000,000.0	25,700,000
Change in income tax payable		(190,800,000)	367,900,000	(2,200,000)
Operating cash flows related to discontinued operations		0	0	9,300,000
Net cash provided by operating activities		1,674,800,000	1,419,600,000	1,059,500,000
Cash flows from investing activities:
Purchases of available-for-sale investments		(167,700,000)	(1,594,800,000)	(500,300,000)
Maturities of available-for-sale investments		78,000,000.0	786,700,000	400,000
Sales of available-for-sale investments		1,376,600,000	0	470,200,000
Sale of equity method investment		0	0	1,700,000
Acquisition of Atmel, net of cash acquired		0	0	(2,747,500,000)
Acquisition of Microsemi, net of cash acquired		(7,850,600,000)	0	0
Investments in other assets		(18,600,000)	(7,100,000)	(10,200,000)
Proceeds from sale of assets		200,000	10,300,000	23,000,000.0
Capital expenditures		(228,900,000)	(206,800,000)	(75,300,000)
Net cash used in investing activities		(6,811,000,000.0)	(1,011,700,000)	(2,838,000,000.0)
Cash flows from financing activities:
Proceeds from issuance of 2017 Senior Convertible Debt	[1]	0	0	2,070,000,000.0
Proceeds from issuance of 2017 Junior Convertible Debt	[1]	0	0	575,000,000.0
Payments on settlement of convertible debt	[1]	0	(73,400,000)	(436,200,000)
Proceeds from issuance of 2023 and 2021 Senior Notes	[1]	1,989,500,000	0	0
Repayment of debt assumed in Microsemi acquisition	[1]	(2,056,900,000)	0	0
Deferred financing costs	[1]	(72,700,000)	(1,200,000)	(36,900,000)
Payment of cash dividends	[1]	(344,400,000)	(337,500,000)	(315,400,000)
Proceeds from sale of common stock	[1]	42,600,000	42,000,000.0	42,200,000
Tax payments related to shares withheld for vested restricted stock units	[1]	(71,800,000)	(44,400,000)	(58,400,000)
Capital lease payments	[1]	(800,000)	(800,000)	(800,000)
Net cash provided by (used in) financing activities		4,663,500,000	(415,300,000)	595,500,000
Effect of foreign exchange rate changes on cash and cash equivalents		0	0	(1,000,000.0)
Net decrease in cash and cash equivalents		(472,700,000)	(7,400,000)	(1,184,000,000.0)
Cash and cash equivalents, and restricted cash at beginning of period	[2]	901,300,000	908,700,000	2,092,700,000
Cash and cash equivalents, and restricted cash at end of period	[2]	428,600,000	901,300,000	908,700,000
Revolving Credit Facility
Cash flows from financing activities:
Proceeds from long-term lines of credit	[1]	4,416,500,000	187,000,000.0	1,537,000,000.0
Repayments of long-term lines of credit	[1]	(1,150,000,000.0)	(187,000,000.0)	(2,781,000,000.0)
Term Loan Facility
Cash flows from financing activities:
Proceeds from long-term lines of credit	[1]	3,000,000,000.0	0	0
Repayments of long-term lines of credit	[1]	$ (1,088,500,000)	$ 0	$ 0

[1] During the fiscal year ended March 31, 2018, the Company issued $111.3 million principal amount of 2017 Junior Convertible Notes and 3.2 million shares of common stock in exchange for $111.3 million principal amount of 2007 Junior Convertible Notes. Refer to Note 12 Debt and Credit Facility for further discussion.

[2] During the fiscal year ended March 31, 2019, the Company adopted ASU 2016-18 - Statement of Cash Flows: Restricted Cash. The following table presents the balance of restricted cash which consists of cash denominated in a foreign currency and restricted in use due to a foreign taxing authority requirement (in millions):
  Year ended March 31,   2019   2018   2017 Restricted cash $ 38.4
  $ 42.1
  $ —