Available-for-Sale Debt Securities - Summary of Available-for-Sale Debt Securities at Estimated Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Available-for-Sale Debt Securities
Total	$ 14,884	$ 16,499
Gross Unrealized Gains	53	2
Gross Unrealized Losses	(2)	(1)
Estimated Fair Value	14,935	16,500
U.S. treasury securities
Available-for-Sale Debt Securities
Total	2,479	2,433
Gross Unrealized Gains	19	0
Gross Unrealized Losses	0	0
Estimated Fair Value	2,498	2,433
Certificates of deposit
Available-for-Sale Debt Securities
Total	2,783	3,517
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	2,783	3,517
U.S. government agencies securities
Available-for-Sale Debt Securities
Total	101	1,081
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	101	1,081
Non-U.S. government securities
Available-for-Sale Debt Securities
Total	145	174
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	145	174
Corporate debt securities
Available-for-Sale Debt Securities
Total	8,755	9,203
Gross Unrealized Gains	31	2
Gross Unrealized Losses	(2)	(1)
Estimated Fair Value	8,784	9,204
Residential mortgage and asset-backed securities
Available-for-Sale Debt Securities
Total	621	91
Gross Unrealized Gains	3	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 624	$ 91

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on 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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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on 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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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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Amount 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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