Investments (Schedule of Held-to-Maturity Securities) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	$ 0
Debt Securities, Held-to-maturity, Unrealized Loss Position, Fair Value		$ 0
Maximum
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity, Unrealized Loss Position, Accumulated Loss	1
Corporate And Other Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	3
Commercial Paper [Member]
Schedule of Held-to-maturity Securities [Line Items]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	7
Short-term Investments [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity investment securities	23	14
Fair Value	23	14
Short-term Investments [Member] \| Corporate And Other Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity investment securities	3	14
Fair Value	3	14
Short-term Investments [Member] \| Commercial Paper [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity investment securities	20	0
Fair Value	$ 20	$ 0

Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity), in unrealized loss position.

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Fair value of investment in debt security measured at amortized cost (held-to-maturity), in unrealized loss position.

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Fair value of investment in debt security measured at amortized cost (held-to-maturity), in continuous unrealized loss position for less than 12 months.

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Fair value of investment in debt security measured at amortized cost (held-to-maturity), in continuous unrealized loss position for 12 months or longer.

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Amount, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity), classified as current.

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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