CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions		3 Months Ended			6 Months Ended			12 Months Ended
		Sep. 30, 2018		Sep. 30, 2017	Sep. 30, 2018		Sep. 30, 2017	Mar. 31, 2018		Mar. 31, 2017
Cash flows from operating activities:
Net income		$ 96.3		$ 189.2	$ 132.0		$ 359.7
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization					393.8		304.4
Deferred income taxes					(71.6)		(46.9)
Share-based compensation expense related to equity incentive plans					87.9		46.0
Loss on settlement of debt		4.1		0.0	4.1		13.8			$ 43.9
Amortization of debt discount on convertible debt					55.4		52.3
Amortization of debt issuance costs					8.4		3.3
Losses on equity method investments		0.1		0.1	0.1		0.1
Gains on sale of assets					0.0		(5.4)
Impairment of intangible assets		1.2			3.1		0.2
Losses on available-for-sale investments, net					6.2		0.0
Amortization of premium on available-for-sale investments					(0.2)		0.6
Changes in operating assets and liabilities, excluding impact of acquisitions:
Decrease (increase) in accounts receivable					65.4		(67.0)
Decrease (increase) in inventories					261.5		(40.1)
Increase in deferred income on shipments to distributors					0.0		31.5
(Decrease) increase in accounts payable and accrued liabilities					(37.8)		25.9
Change in other assets and liabilities					(25.1)		(0.7)
Change in income tax payable					(93.3)		17.4
Net cash provided by operating activities					789.9		695.1
Cash flows from investing activities:
Purchases of available-for-sale investments					(167.7)		(879.4)
Maturities of available-for-sale investments					75.9		363.0
Sales of available-for-sale investments					1,376.6		0.0
Acquisition of Microsemi, net of cash acquired					(7,850.6)		0.0
Investments in other assets					(8.9)		(3.8)
Proceeds from sale of assets					0.1		10.2
Capital expenditures					(161.4)		(82.0)
Net cash used in investing activities					(6,736.0)		(592.0)
Cash flows from financing activities:
Payments on settlement of convertible debt	[1]				0.0		(15.2)
Proceeds from Issuance of 2023 and 2021 Senior Notes	[1]				1,989.5		0.0
Proceeds from borrowings on Term Loan Facility	[1]				3,000.0		0.0
Repayments of term loan facility	[1]				(267.0)		0.0
Proceeds from borrowings on revolving loan under credit facility	[1]				3,632.5		113.0
Repayments of revolving loan under credit facility	[1]				(532.5)		(113.0)
Repayment of debt assumed in Microsemi acquisition	[1]				(2,056.9)		0.0
Deferred financing costs	[1]				(72.7)		(0.8)
Payment of cash dividends	[1]				(171.4)		(167.4)
Proceeds from sale of common stock	[1]				20.3		19.6
Tax payments related to shares withheld for vested restricted stock units	[1]				(36.9)		(21.2)
Capital lease payments	[1]				(0.4)		(0.4)
Net cash provided by (used in) financing activities	[1]				5,504.5		(185.4)
Net decrease in cash, cash equivalents, and restricted cash					(441.6)		(82.3)
Cash and cash equivalents, and restricted cash at beginning of period	[2]				901.3	[1]	908.7	$ 908.7
Cash and cash equivalents, and restricted cash at end of period	[2]	$ 459.7	[1]	$ 826.4	$ 459.7	[1]	$ 826.4	$ 901.3	[1]	$ 908.7

[1] During the six months ended September 30, 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 September 30, 2017 March 31, 2018 September 30, 2018Restricted cash $— $40.2 $42.1 $40.0