Investments in Marketable Securities - Summary of Investments in Marketable Securities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Mar. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	$ 876	$ 1,381
Available-for-sale debt securities, Unrealized gains	36	30
Available-for-sale debt securities, Unrealized losses	(3)	(10)
Available-for-sale debt securities, Fair value	909	1,401
Equity investments, Fair value	3,405	2,419
Investments in marketable securities total	4,314	3,820
U.S. government and agency obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	197	160
Available-for-sale debt securities, Unrealized gains	10	16
Available-for-sale debt securities, Unrealized losses	0	0
Available-for-sale debt securities, Fair value	207	176
Municipal debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	10	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	12	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	362	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	362	601
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	163	188
Available-for-sale debt securities, Unrealized gains	17	10
Available-for-sale debt securities, Unrealized losses	0	(1)
Available-for-sale debt securities, Fair value	180	197
U.S. government agency mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	41	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	43	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	(3)	(2)
Available-for-sale debt securities, Fair value	46	45
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	55	75
Available-for-sale debt securities, Unrealized gains	3	0
Available-for-sale debt securities, Unrealized losses	0	(3)
Available-for-sale debt securities, Fair value	$ 58	$ 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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