Fair Value Measurements (Details) - USD ($)	Jun. 30, 2021	Mar. 31, 2021
Recurring | Fair value, inputs, level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in money market funds	$ 521,000,000	$ 1,600,000,000
Recurring | Fair value, inputs, level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying amount of liabilities	7,176,000,000	7,148,000,000
Estimated fair values of liabilities	7,865,000,000	7,785,000,000
Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value	$ 0	$ 0