Fair Value of Financial Instruments - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	$ 13,905	$ 1,606
Money market funds (Cash and cash equivalents) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial assets, Fair Value	13,847	1,632
Interest Rate Swap Assets (Liabilities) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial assets, Fair Value		1
Financial liabilities, Fair Value	58	(27)
Level I [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	13,847	1,632
Level I [Member] | Money market funds (Cash and cash equivalents) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial assets, Fair Value	13,847	1,632
Level II [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	58	(26)
Level II [Member] | Interest Rate Swap Assets (Liabilities) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial assets, Fair Value		1
Financial liabilities, Fair Value	$ 58	$ (27)