Available-for-Sale Debt Securities - Summary of Available-for-Sale Debt Securities at Estimated Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Available-for-Sale Securities
Amortized Cost	$ 2,023	$ 16,499
Gross Unrealized Gains	3	2
Gross Unrealized Losses	0	(1)
Available-for-sale debt securities	2,026	16,500
U.S. treasury securities
Available-for-Sale Securities
Amortized Cost	308	2,433
Gross Unrealized Gains	1	0
Gross Unrealized Losses	0	0
Available-for-sale debt securities	309	2,433
Certificates of deposit
Available-for-Sale Securities
Amortized Cost	216	3,517
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Available-for-sale debt securities	216	3,517
U.S. government agencies securities
Available-for-Sale Securities
Amortized Cost	0	1,081
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Available-for-sale debt securities	0	1,081
Non-U.S. government securities
Available-for-Sale Securities
Amortized Cost	43	174
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Available-for-sale debt securities	43	174
Corporate debt securities
Available-for-Sale Securities
Amortized Cost	1,140	9,203
Gross Unrealized Gains	2	2
Gross Unrealized Losses	0	(1)
Available-for-sale debt securities	1,142	9,204
Residential mortgage and asset-backed securities
Available-for-Sale Securities
Amortized Cost	316	91
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Available-for-sale debt securities	$ 316	$ 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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