Investments - Narrative (Details) - USD ($)		12 Months Ended
	Jul. 19, 2018	Sep. 30, 2019
Debt and Equity Securities, FV-NI [Line Items]
Purchases of investments, amount outstanding		$ 0
PTC
Debt and Equity Securities, FV-NI [Line Items]
Number of shares purchased (in shares)	10,582,010
Purchase of stock price (usd per share)	$ 94.50
Consideration paid to purchase stock	$ 1,000,000,000.0
Entity specific transfer restrictions, period	3 years
Sale of stock, subsequent trading period	90 days
Fair value of PTC shares		721,500,000
Loss on fair value of PTC shares		$ 368,500,000
PTC | Minimum
Debt and Equity Securities, FV-NI [Line Items]
Percentage of total outstanding common stock, that can be traded in future periods	1.00%
PTC | Maximum
Debt and Equity Securities, FV-NI [Line Items]
Percentage of total outstanding common stock, that can be traded in future periods	2.00%