Available-for-Sale Debt Securities - Summary of Available-for-Sale Debt Securities at Estimated Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Available-for-Sale Debt Securities
Total	$ 13,365	$ 16,499
Gross Unrealized Gains	35	2
Gross Unrealized Losses	(1)	(1)
Estimated Fair Value	13,399	16,500
U.S. treasury securities
Available-for-Sale Debt Securities
Total	2,225	2,433
Gross Unrealized Gains	13	0
Gross Unrealized Losses	0	0
Estimated Fair Value	2,238	2,433
Certificates of deposit
Available-for-Sale Debt Securities
Total	2,136	3,517
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	2,136	3,517
U.S. government agencies securities
Available-for-Sale Debt Securities
Total	71	1,081
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	71	1,081
Non-U.S. government securities
Available-for-Sale Debt Securities
Total	220	174
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	220	174
Corporate debt securities
Available-for-Sale Debt Securities
Total	7,506	9,203
Gross Unrealized Gains	20	2
Gross Unrealized Losses	(1)	(1)
Estimated Fair Value	7,525	9,204
Residential mortgage and asset-backed securities
Available-for-Sale Debt Securities
Total	1,207	91
Gross Unrealized Gains	2	0
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 1,209	$ 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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