CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)		3 Months Ended				9 Months Ended		12 Months Ended
		Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Mar. 31, 2019
Cash flows from operating activities:
Net income		$ 311,100,000	$ 50,700,000	$ 49,200,000	$ 35,700,000	$ 470,700,000	$ 181,200,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization						904,700,000	637,700,000
Deferred income taxes						(404,200,000)	(29,100,000)
Share-based compensation expense related to equity incentive plans						129,500,000	127,500,000
Loss on settlement of debt		0		200,000		2,000,000.0	4,300,000
Amortization of debt discount						90,900,000	85,200,000
Amortization of debt issuance costs						12,800,000	12,100,000
Losses on equity method investments		0		100,000		0	200,000
Losses on sale of assets						400,000	0
Losses on write-down of fixed assets						2,700,000	500,000
Impairment of intangible assets		0		0		500,000	3,100,000
(Gains) losses on available-for-sale investments and marketable equity securities, net						(1,000,000.0)	6,800,000
Amortization of premium on available-for-sale investments						0	(200,000)
Changes in operating assets and liabilities, excluding impact of acquisitions:
Decrease in accounts receivable						73,200,000	189,400,000
Decrease in inventories						5,600,000	344,500,000
Decrease in accounts payable and accrued liabilities						(53,300,000)	(143,500,000)
Change in other assets and liabilities						(3,900,000)	15,200,000
Change in income tax payable						(58,500,000)	(163,500,000)
Net cash provided by operating activities						1,172,100,000	1,271,400,000
Cash flows from investing activities:
Purchases of available-for-sale investments						(2,000,000.0)	(167,700,000)
Maturities of available-for-sale investments						0	75,700,000
Sales of available-for-sale investments						0	1,376,600,000
Acquisition of Microsemi, net of cash acquired						0	(7,850,600,000)
Investments in other assets						(40,500,000)	(12,800,000)
Proceeds from sale of assets						500,000	200,000
Capital expenditures						(55,700,000)	(188,800,000)
Net cash used in investing activities						(97,700,000)	(6,767,400,000)
Cash flows from financing activities:
Proceeds from issuance of 2023 and 2021 Senior Notes						0	1,989,500,000
Repayment of debt assumed in Microsemi acquisition						0	(2,056,900,000)
Deferred financing costs						(1,800,000)	(72,700,000)
Payment of cash dividends						(262,100,000)	(257,800,000)
Proceeds from sale of common stock						38,800,000	26,900,000
Tax payments related to shares withheld for vested restricted stock units						(50,200,000)	(57,000,000.0)
Capital lease payments						(600,000)	(600,000)
Net cash (used in) provided by financing activities						(1,105,900,000)	5,026,900,000
Net decrease in cash and cash equivalents						(31,500,000)	(469,100,000)
Cash and cash equivalents, and restricted cash at beginning of period	[1]		$ 428,600,000		$ 901,300,000	428,600,000	901,300,000	$ 901,300,000
Cash and cash equivalents, and restricted cash at end of period	[1]	397,100,000		$ 432,200,000		397,100,000	432,200,000	428,600,000
Non-cash activities:
Right-of-use assets obtained in exchange of lease liabilities						25,100,000	0
Cash paid for:
Operating lease payments in operating cash flows						39,300,000	0
Restricted Cash		$ 0				0		$ 38,400,000
Term Loan Facility
Cash flows from financing activities:
Proceeds from borrowings under credit facility						0	3,000,000,000.0
Repayments of credit facility						(188,000,000.0)	(287,000,000.0)
Revolving Credit Facility
Cash flows from financing activities:
Proceeds from borrowings under credit facility						682,000,000.0	3,725,500,000
Repayments of credit facility						$ (1,324,000,000.0)	$ (983,000,000.0)

[1] Schedule of 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):
  December 31,   March 31,   2019   2019 Restricted cash $ —
  $ 38.4