Income Taxes - Effective Tax Rate Reconciliation, Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Income Tax Rate Reconciliation [Line Items]
Effective income tax rate reconciliation, divestiture of business, amount	$ 344
Effective income tax rate reconciliation, divestiture of business, percent	52.60%	0.00%	0.00%
Effective income tax rate reconciliation, change in deferred tax assets valuation allowance, amount	$ 1,565	$ 631	$ 256
Effective income tax rate reconciliation, change in deferred tax assets valuation allowance, percent	239.30%	(12.10%)	16.90%
Effective income tax rate reconciliation, change in tax credits, amount	$ 319	$ 135
Effective income tax rate reconciliation, decrease from tax credits, percent	48.70%	(2.60%)	0.60%
Effective income tax rate reconciliation, uncertain tax positions, amount	$ 112
Effective income tax rate reconciliation, uncertain tax positions, percent	17.20%	(1.10%)	(1.50%)
Effective income tax rate reconciliation, goodwill impairment charge, amount		$ 1,482
Effective income tax rate reconciliation, goodwill impairment charge, percent	0.00%	(28.30%)	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	0.00%	(3.60%)	0.00%
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%
Luxembourg
Income Tax Rate Reconciliation [Line Items]
Effective income tax rate reconciliation, gain (loss) on investments, amount	$ (1,226)	$ (637)	$ 360
Effective income tax rate reconciliation, gain (loss) on investments, percent	(187.50%)	(12.20%)	23.70%