Debt - Additional Information (Details) shares in Millions		1 Months Ended	3 Months Ended			9 Months Ended		12 Months Ended
	Aug. 11, 2020 USD ($) shares	Aug. 31, 2020 USD ($)	Dec. 31, 2021 USD ($)	Sep. 30, 2021 USD ($) shares	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) day trading_day shares	Sep. 30, 2020 USD ($) shares	Dec. 31, 2020 USD ($) shares	Jun. 30, 2017 USD ($)
Debt Instrument [Line Items]
Estimated fair value of the note based on the closing trading price				$ 100		$ 100		$ 100
Percentage of purchase price of notes which should be paid upon fundamental change (percent)						100.00%
Benefit from exercise of 2022 Note Hedge				$ 24,000,000	$ 1,162,000,000	$ 215,000,000	$ 1,184,000,000
Net proceeds from unwind of 2022 Note Hedge						0	1,106,000,000
Loss on extinguishment of 2022 Notes						$ 3,000,000	$ 42,000,000
2022 Warrants
Debt Instrument [Line Items]
Number of shares to be issued upon exercise of the Warrants (in shares) | shares						0.5	2.3	2.3
Warrant exercise period | trading_day						60
Number of potential securities issued upon automatic exercise of the Warrants (in shares) | shares				0.7		0.7
Stock Price Trigger Measurement
Debt Instrument [Line Items]
Trading days threshold | day						20
Consecutive trading days threshold, total | day						30
Threshold percentage of stock price trigger (percent)						130.00%
Notes Price Trigger Measurement
Debt Instrument [Line Items]
Trading days threshold | day						5
Consecutive trading days threshold, total | day						5
Threshold percentage of stock price trigger (percent)						98.00%
Conversion of notes base conversion price						$ 1,000
2030 Notes
Debt Instrument [Line Items]
Stated interest rate		1.40%
Debt term		10 years
Face amount of debt		$ 1,500,000,000		$ 1,500,000,000		1,500,000,000
Percentage of principle issued		0.9963
Payments of debt issuance costs		$ 13,000,000
2022 Notes
Debt Instrument [Line Items]
Stated interest rate									0.00%
Face amount of debt				$ 96,000,000		96,000,000			$ 782,500,000
Equity recorded at time of issuance									$ 160,000,000
Cash paid for settlement of debt						73,000,000
Fair value adjustments						(216,000,000)
Benefit from exercise of 2022 Note Hedge						$ 215,000,000
Repurchased face amount	$ 497,000,000
Net proceeds from unwind of 2022 Note Hedge	1,100,000,000
Extinguishment of debt, amount, debt component	493,000,000
Extinguishment of debt, amount, equity component	1,100,000,000
Loss on extinguishment of 2022 Notes	39,000,000
Unamortized debt discount and unamortized debt issuance costs	$ 43,000,000
Reduction of aggregate number of call options (in shares) | shares	3.7
2022 Notes | Forecast
Debt Instrument [Line Items]
Cash paid for settlement of debt			$ 2,000,000