Financial Instruments and Fair Value Measurements - Summary of Financial Instruments by Significant Categories and Fair Value Measurement on a Recurring Basis (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Fair Value, Financial Instruments [Line Items]
Total investments	$ 547	$ 538
Total cash equivalents and investments and restricted cash equivalents and investments	1,933	2,276
Fair Value Measurement on a Recurring Basis
Fair Value, Financial Instruments [Line Items]
Total cash equivalents	4	25
Total investments	319	303
Total restricted cash equivalents	94	94
Total restricted investments	228	235
Total cash equivalents and investments and restricted cash equivalents and investments	645	657
Fair Value Measurement on a Recurring Basis \| Level 1
Fair Value, Financial Instruments [Line Items]
Total cash equivalents	4	4
Total investments	0	0
Total restricted cash equivalents	90	93
Total restricted investments	0	0
Total cash equivalents and investments and restricted cash equivalents and investments	94	97
Fair Value Measurement on a Recurring Basis \| Level 2
Fair Value, Financial Instruments [Line Items]
Total cash equivalents	0	21
Total investments	319	303
Total restricted cash equivalents	4	1
Total restricted investments	228	235
Total cash equivalents and investments and restricted cash equivalents and investments	551	560
Money market mutual funds \| Fair Value Measurement on a Recurring Basis
Fair Value, Financial Instruments [Line Items]
Total cash equivalents	4	4
Total restricted cash equivalents	90	93
Money market mutual funds \| Fair Value Measurement on a Recurring Basis \| Level 1
Fair Value, Financial Instruments [Line Items]
Total cash equivalents	4	4
Total restricted cash equivalents	90	93
Money market mutual funds \| Fair Value Measurement on a Recurring Basis \| Level 2
Fair Value, Financial Instruments [Line Items]
Total cash equivalents	0	0
Total restricted cash equivalents	0	0
U.S. treasuries \| Fair Value Measurement on a Recurring Basis
Fair Value, Financial Instruments [Line Items]
Total cash equivalents	0	21
Total restricted cash equivalents	4
U.S. treasuries \| Fair Value Measurement on a Recurring Basis \| Level 1
Fair Value, Financial Instruments [Line Items]
Total cash equivalents	0	0
Total restricted cash equivalents	0
U.S. treasuries \| Fair Value Measurement on a Recurring Basis \| Level 2
Fair Value, Financial Instruments [Line Items]
Total cash equivalents	0	21
Total restricted cash equivalents	4
Certificate of deposits \| Fair Value Measurement on a Recurring Basis
Fair Value, Financial Instruments [Line Items]
Total restricted cash equivalents		1
Certificate of deposits \| Fair Value Measurement on a Recurring Basis \| Level 1
Fair Value, Financial Instruments [Line Items]
Total restricted cash equivalents		0
Certificate of deposits \| Fair Value Measurement on a Recurring Basis \| Level 2
Fair Value, Financial Instruments [Line Items]
Total restricted cash equivalents		1
Asset-backed securities
Fair Value, Financial Instruments [Line Items]
Total investments	45	49
Asset-backed securities \| Fair Value Measurement on a Recurring Basis
Fair Value, Financial Instruments [Line Items]
Total investments	45	49
Asset-backed securities \| Fair Value Measurement on a Recurring Basis \| Level 1
Fair Value, Financial Instruments [Line Items]
Total investments	0	0
Asset-backed securities \| Fair Value Measurement on a Recurring Basis \| Level 2
Fair Value, Financial Instruments [Line Items]
Total investments	45	49
Corporate bonds
Fair Value, Financial Instruments [Line Items]
Total investments	166	167
Corporate bonds \| Fair Value Measurement on a Recurring Basis
Fair Value, Financial Instruments [Line Items]
Total investments	137	137
Total restricted investments	29	30
Corporate bonds \| Fair Value Measurement on a Recurring Basis \| Level 1
Fair Value, Financial Instruments [Line Items]
Total investments	0	0
Total restricted investments	0	0
Corporate bonds \| Fair Value Measurement on a Recurring Basis \| Level 2
Fair Value, Financial Instruments [Line Items]
Total investments	137	137
Total restricted investments	29	30
U.S. government agencies and government- sponsored agencies
Fair Value, Financial Instruments [Line Items]
Total investments	15	17
U.S. government agencies and government- sponsored agencies \| Fair Value Measurement on a Recurring Basis
Fair Value, Financial Instruments [Line Items]
Total investments	2	2
Total restricted investments	13	15
U.S. government agencies and government- sponsored agencies \| Fair Value Measurement on a Recurring Basis \| Level 1
Fair Value, Financial Instruments [Line Items]
Total investments	0	0
Total restricted investments	0	0
U.S. government agencies and government- sponsored agencies \| Fair Value Measurement on a Recurring Basis \| Level 2
Fair Value, Financial Instruments [Line Items]
Total investments	2	2
Total restricted investments	13	15
U.S. treasuries
Fair Value, Financial Instruments [Line Items]
Total investments	302	285
U.S. treasuries \| Fair Value Measurement on a Recurring Basis
Fair Value, Financial Instruments [Line Items]
Total investments	127	106
Total restricted investments	175	179
U.S. treasuries \| Fair Value Measurement on a Recurring Basis \| Level 1
Fair Value, Financial Instruments [Line Items]
Total investments	0	0
Total restricted investments	0	0
U.S. treasuries \| Fair Value Measurement on a Recurring Basis \| Level 2
Fair Value, Financial Instruments [Line Items]
Total investments	127	106
Total restricted investments	175	179
Other debt securities
Fair Value, Financial Instruments [Line Items]
Total investments	8	9
Other debt securities \| Fair Value Measurement on a Recurring Basis
Fair Value, Financial Instruments [Line Items]
Total investments	8	9
Other debt securities \| Fair Value Measurement on a Recurring Basis \| Level 1
Fair Value, Financial Instruments [Line Items]
Total investments	0	0
Other debt securities \| Fair Value Measurement on a Recurring Basis \| Level 2
Fair Value, Financial Instruments [Line Items]
Total investments	8	9
Certificate of deposits
Fair Value, Financial Instruments [Line Items]
Total investments	11	11
Certificate of deposits \| Fair Value Measurement on a Recurring Basis
Fair Value, Financial Instruments [Line Items]
Total restricted investments	11	11
Certificate of deposits \| Fair Value Measurement on a Recurring Basis \| Level 1
Fair Value, Financial Instruments [Line Items]
Total restricted investments	0	0
Certificate of deposits \| Fair Value Measurement on a Recurring Basis \| Level 2
Fair Value, Financial Instruments [Line Items]
Total restricted investments	$ 11	$ 11

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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