CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)		3 Months Ended		9 Months Ended		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net income		$ 49,200,000	$ (251,100,000)	$ 181,200,000	$ 108,700,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization				637,700,000	459,000,000
Deferred income taxes				(29,100,000)	67,600,000
Share-based compensation expense related to equity incentive plans				127,500,000	70,000,000
Loss on settlement of debt		200,000	2,100,000	4,300,000	16,000,000		$ 43,900,000
Amortization of debt discount				85,200,000	79,000,000
Amortization of debt issuance costs				12,100,000	5,000,000
Losses on equity method investments		100,000	100,000	200,000	200,000
Gains on sale of assets				0	(5,400,000)
Losses on write-down of fixed assets				500,000	100,000
Impairment of intangible assets				3,100,000	300,000
Losses on available-for-sale investments and marketable equity securities, net				6,800,000	0
Amortization of premium on available-for-sale investments				(200,000)	500,000
Changes in operating assets and liabilities, excluding impact of acquisitions:
Decrease (increase) in accounts receivable				189,400,000	(74,800,000)
Decrease (increase) in inventories				344,500,000	(70,200,000)
Increase in deferred income on shipments to distributors				0	42,900,000
(Decrease) increase in accounts payable and accrued liabilities				(143,500,000)	41,800,000
Change in other assets and liabilities				15,200,000	15,500,000
Change in income tax payable				(163,500,000)	303,900,000
Net cash provided by operating activities				1,271,400,000	1,060,100,000
Cash flows from investing activities:
Purchases of available-for-sale investments				(167,700,000)	(1,338,100,000)
Maturities of available-for-sale investments				75,700,000	520,000,000
Sales of available-for-sale investments				1,376,600,000	0
Acquisition of Microsemi, net of cash acquired				(7,850,600,000)	0
Investments in other assets				(12,800,000)	(5,400,000)
Proceeds from sale of assets				200,000	10,300,000
Capital expenditures				(188,800,000)	(148,400,000)
Net cash used in investing activities				(6,767,400,000)	(961,600,000)
Cash flows from financing activities:
Payments on settlement of convertible debt	[1]			0	(73,400,000)
Proceeds from Issuance of 2023 and 2021 Senior Notes	[1]			1,989,500,000	0
Proceeds from borrowings on Term Loan Facility	[1]			3,000,000,000	0
Repayments of term loan facility	[1]			(287,000,000)	0
Proceeds from borrowings on revolving loan under credit facility	[1]			3,725,500,000	187,000,000
Repayments of revolving loan under credit facility	[1]			(983,000,000)	(187,000,000)
Repayment of debt assumed in Microsemi acquisition	[1]			(2,056,900,000)	0
Deferred financing costs	[1]			(72,700,000)	(1,200,000)
Payment of cash dividends	[1]			(257,800,000)	(252,400,000)
Proceeds from sale of common stock	[1]			26,900,000	26,600,000
Tax payments related to shares withheld for vested restricted stock units	[1]			(57,000,000)	(34,100,000)
Capital lease payments	[1]			(600,000)	(600,000)
Net cash provided by (used in) financing activities				5,026,900,000	(335,100,000)
Net decrease in cash, cash equivalents, and restricted cash				(469,100,000)	(236,600,000)
Cash and cash equivalents, and restricted cash at beginning of period	[2]			901,300,000	908,700,000	$ 908,700,000
Cash and cash equivalents, and restricted cash at end of period	[2]	$ 432,200,000	$ 672,100,000	$ 432,200,000	$ 672,100,000	$ 901,300,000	$ 908,700,000

[1] During the nine months ended December 31, 2017, the Company issued $111.3 million principal amount of 2017 Junior Convertible Debt and 3.2 million shares of common stock in exchange for $111.3 million principal amount of 2007 Junior Convertible Debt. Refer to Note 13 Debt and Credit Facility for further discussion.

[2] In the three months ended June 30, 2018, 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): As of March 31, 2017 December 31, 2017 March 31, 2018 December 31, 2018Restricted cash $— $40.8 $42.1 $39.1