Income Taxes - Effective Tax Rate Reconciliation, Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Income Tax Rate Reconciliation [Line Items]
Effective income tax rate reconciliation, goodwill impairment charge, amount	$ 1,482
Effective income tax rate reconciliation, goodwill impairment charge, percent	(28.30%)	0.00%	0.00%
Effective income tax rate reconciliation, non-taxable gain on arbitration award, amount	$ 186
Effective income tax rate reconciliation, non-taxable gain on arbitration award, percent	(3.60%)	0.00%	0.00%
Effective income tax rate reconciliation, change in deferred tax assets valuation allowance, amount	$ 631	$ 256
Effective income tax rate reconciliation, change in deferred tax assets valuation allowance, percent	(12.10%)	16.90%	(7.70%)
Effective income tax rate reconciliation, change in tax credits, amount	$ 135
Effective income tax rate reconciliation, change in tax credits, percent	(2.60%)	0.60%	7.60%
Effective income tax rate reconciliation, change in deferred revenue accounting method, amount		$ 66
Effective income tax rate reconciliation, change in deferred revenue accounting method, percent		4.30%
Effective income tax rate reconciliation, foreign subsidiary basis, amount			$ (554)
Effective income tax rate reconciliation, foreign subsidiary basis, percentage			(42.50%)
Effective income tax rate reconciliation, Tax Cuts and Jobs Act of 2017, transition tax on accumulated foreign earnings, amount			$ 361
Effective income tax rate reconciliation, Tax Cuts and Jobs Act of 2017, transition tax on accumulated foreign earnings, percent			0.277
Effective income tax rate reconciliation, remeasurement of deferred tax assets and liabilities, amount			$ (338)
Effective income tax rate reconciliation, remeasurement of deferred tax assets and liabilities, percent			(25.90%)
Luxembourg
Income Tax Rate Reconciliation [Line Items]
Effective income tax rate reconciliation, gain (loss) on investments, amount	$ (637)	$ 360
Effective income tax rate reconciliation, gain (loss) on investments, percent	(12.20%)	23.70%