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Fair Value Measurements Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021 USD ($) Loans	Dec. 31, 2020 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Agreements Not Publicly Held | Loans	5
1.250 Convertible Senior Notes due 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Convertible, Conversion Ratio	25.9909
1.250 Convertible Senior Notes due 2025 | Unsecured Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stated interest rate	1.25%
1.250 Convertible Senior Notes due 2025 | Convertible Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Convertible, Carrying Amount of Equity Component | $	$ 403	$ 403

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