Available-for-Sale Debt Securities - Summary of Available-for-Sale Debt Securities by Contractual Maturity (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Amortized Cost
Within one year	$ 16,858
After one year through five years	2,166
After five years through ten years	14
After ten years	14
Amortized Cost	19,052	$ 24,216
Fair Value
Within one year	16,859
After one year through five years	2,166
After five years through ten years	14
After ten years	14
Available-for-sale debt securities	$ 19,053	$ 24,164

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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