Investments in Marketable Securities - Summary of Investments in Marketable Securities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Mar. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	$ 724	$ 1,381
Available-for-sale debt securities, Unrealized gains	37	30
Available-for-sale debt securities, Unrealized losses	(4)	(10)
Available-for-sale debt securities, Fair value	757	1,401
Equity investments, Fair value	3,839	2,419
Investments in marketable securities total	4,596	3,820
U.S. government and agency obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	223	160
Available-for-sale debt securities, Unrealized gains	9	16
Available-for-sale debt securities, Unrealized losses	(2)	0
Available-for-sale debt securities, Fair value	230	176
Municipal debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	8	9
Available-for-sale debt securities, Unrealized gains	2	2
Available-for-sale debt securities, Unrealized losses	0	0
Available-for-sale debt securities, Fair value	10	11
Certificates of deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost		250
Available-for-sale debt securities, Unrealized gains		0
Available-for-sale debt securities, Unrealized losses		(1)
Available-for-sale debt securities, Fair value		249
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	200	604
Available-for-sale debt securities, Unrealized gains	0	0
Available-for-sale debt securities, Unrealized losses	0	(3)
Available-for-sale debt securities, Fair value	200	601
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	159	188
Available-for-sale debt securities, Unrealized gains	18	10
Available-for-sale debt securities, Unrealized losses	0	(1)
Available-for-sale debt securities, Fair value	177	197
U.S. government agency mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	35	47
Available-for-sale debt securities, Unrealized gains	2	2
Available-for-sale debt securities, Unrealized losses	0	0
Available-for-sale debt securities, Fair value	37	49
Non-agency residential mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	1	1
Available-for-sale debt securities, Unrealized gains	0	0
Available-for-sale debt securities, Unrealized losses	0	0
Available-for-sale debt securities, Fair value	1	1
Non-agency commercial mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	47	47
Available-for-sale debt securities, Unrealized gains	2	0
Available-for-sale debt securities, Unrealized losses	(2)	(2)
Available-for-sale debt securities, Fair value	47	45
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	51	75
Available-for-sale debt securities, Unrealized gains	4	0
Available-for-sale debt securities, Unrealized losses	0	(3)
Available-for-sale debt securities, Fair value	$ 55	$ 72

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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