Fair Value Measurements (Details) - USD ($)	Jun. 30, 2020	Mar. 31, 2020
Recurring | Fair value, inputs, level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying amount of liabilities	$ 7,400,000,000	$ 7,400,000,000
Estimated fair values of liabilities	8,100,000,000	7,800,000,000
Recurring | Fair value, inputs, level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in money market funds	139,000,000	2,000,000,000.0
Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	0	0
Liabilities measured at fair value	$ 0	$ 0