Fair Value of Financial Instruments - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	$ 11,514	$ 13,905
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	11,477	13,847
Interest Rate Swap Assets (Liabilities) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial liabilities, Fair Value	37	58
Level I [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	11,477	13,847
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	11,477	13,847
Level I [Member] | Interest Rate Swap Assets (Liabilities) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial liabilities, Fair Value	0	0
Level II [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	37	58
Level II [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	0	0
Level II [Member] | Interest Rate Swap Assets (Liabilities) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial liabilities, Fair Value	37	58
Level III [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total	0	0
Level III [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	0	0
Level III [Member] | Interest Rate Swap Assets (Liabilities) [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Financial liabilities, Fair Value	$ 0	$ 0