Fair Value Measurements - Schedule of Long-Term Debt is Recorded at Amortized Cost (Details) - Recurring - Fair value, inputs, level 2 - USD ($) $ in Millions	Sep. 30, 2021	Mar. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying amount of liabilities	$ 5,985	$ 7,148
Estimated fair values of liabilities	$ 6,496	$ 7,785