Debt and Credit Facility - Credit Facility (Details)		1 Months Ended	3 Months Ended		6 Months Ended
	May 18, 2018 USD ($)	May 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Jun. 01, 2018 USD ($)	Mar. 31, 2018 USD ($)	Feb. 28, 2017 USD ($)
Line of Credit Facility [Line Items]
Debt issuance costs		$ 24,400,000	$ 101,200,000		$ 101,200,000			$ 40,100,000	$ 33,700,000
Interest expense			138,600,000	$ 49,500,000	$ 229,000,000	$ 98,900,000
2015 Senior Convertible Debt
Line of Credit Facility [Line Items]
Remaining period, in years, over which unamortized debt discount will be recognized as non-cash interest expense (in years)					6 years 4 months 16 days
Debt issuance costs			13,800,000		$ 13,800,000			14,800,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Debt issuance costs			16,500,000		16,500,000			5,900,000
Loans terminated			244,300,000
Term Loan Facility
Line of Credit Facility [Line Items]
Debt issuance costs			30,000,000		30,000,000			0
Revolving credit facility
Line of Credit Facility [Line Items]
Credit agreement maximum borrowing amount	$ 3,600,000,000	3,840,000,000.00					$ 3,600,000,000.0	$ 3,122,000,000.000
Debt issuance costs		13,600,000
Interest expense			34,700,000	$ 2,300,000	49,500,000	$ 5,000,000
Credit Agreement, total consolidated debt, maximum			$ 700,000,000		$ 700,000,000
Interest coverage ratio			3.25		3.25
Interest rate spread on overdue principal in event of default (percentage)			2.00%		2.00%
Interest rate spread on overdue amounts in event of default (percentage)			2.00%		2.00%
Revolving credit facility | 2023 Tranche
Line of Credit Facility [Line Items]
Credit agreement maximum borrowing amount	3,600,000,000
Revolving credit facility | Term Loan Facility
Line of Credit Facility [Line Items]
Debt issuance costs		34,700,000
Proceeds from borrowings on term loan facility		$ 3,000,000,000
Quarterly amortization payments, percent			0.25%		0.25%
Repayments of long-term debt			$ 267,000,000
Foreign line of credit
Line of Credit Facility [Line Items]
Credit agreement maximum borrowing amount	250,000,000
Standby letters of credit
Line of Credit Facility [Line Items]
Credit agreement maximum borrowing amount	50,000,000
Line of credit facility swingline loan sublimit
Line of Credit Facility [Line Items]
Credit agreement maximum borrowing amount	$ 25,000,000
Base Rate | Minimum | Revolving credit facility | 2023 Tranche
Line of Credit Facility [Line Items]
Spread on variable rate (percentage)	0.00%
Base Rate | Maximum | Revolving credit facility | 2023 Tranche
Line of Credit Facility [Line Items]
Spread on variable rate (percentage)	1.00%
London Interbank Offered Rate (LIBOR) | Minimum | Revolving credit facility | 2023 Tranche
Line of Credit Facility [Line Items]
Spread on variable rate (percentage)	1.00%
London Interbank Offered Rate (LIBOR) | Maximum | Revolving credit facility | 2023 Tranche
Line of Credit Facility [Line Items]
Spread on variable rate (percentage)	2.00%
Leverage Ratio Percent Three | Revolving credit facility
Line of Credit Facility [Line Items]
Credit agreement, total leverage ratio, maximum			5.75		5.75
Credit agreement, total leverage ratio, temporary maximum allowed, next three quarters			3.75		3.75
Leverage Ratio Percent Three | Revolving credit facility | Term Loan Facility
Line of Credit Facility [Line Items]
Mandatory prepayment of excess cash flow, percentage			0.00%		0.00%
Leverage Ratio Percent One | Revolving credit facility
Line of Credit Facility [Line Items]
Credit agreement, total leverage ratio, maximum			6.75		6.75
Credit agreement, total leverage ratio, temporary maximum allowed, next three quarters			4.75		4.75
Leverage Ratio Percent One | Revolving credit facility | Term Loan Facility
Line of Credit Facility [Line Items]
Mandatory prepayment of excess cash flow, percentage			50.00%		50.00%
Leverage Ratio Percent Two | Revolving credit facility
Line of Credit Facility [Line Items]
Credit agreement, total leverage ratio, maximum			6.25		6.25
Credit agreement, total leverage ratio, temporary maximum allowed, next three quarters			4.25		4.25
Leverage Ratio Percent Two | Revolving credit facility | Term Loan Facility
Line of Credit Facility [Line Items]
Mandatory prepayment of excess cash flow, percentage			25.00%		25.00%
Term Loan Facility
Line of Credit Facility [Line Items]
Debt issuance costs			$ 2,900,000		$ 2,900,000