Investments in Marketable Securities - Summary of Investments in Marketable Securities (Details) - USD ($) $ in Millions	Sep. 30, 2019	Mar. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	$ 1,025	$ 629
Available-for-sale debt securities, Unrealized gains	24	8
Available-for-sale debt securities, Unrealized losses	0	(4)
Available-for-sale debt securities, Fair value	1,049	633
Equity investments, Fair value	2,403	2,275
Investments in marketable securities total	3,452	2,908
U.S. government and agency obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	196	213
Available-for-sale debt securities, Unrealized gains	8	2
Available-for-sale debt securities, Unrealized losses	0	(3)
Available-for-sale debt securities, Fair value	204	212
Municipal debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	9	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	11	11
Certificates of deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	150	50
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	150	50
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	350	70
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	350	70
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	164	160
Available-for-sale debt securities, Unrealized gains	10	3
Available-for-sale debt securities, Unrealized losses	0	(1)
Available-for-sale debt securities, Fair value	174	162
U.S. government agency mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	32	35
Available-for-sale debt securities, Unrealized gains	1	0
Available-for-sale debt securities, Unrealized losses	0	0
Available-for-sale debt securities, Fair value	33	35
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	44	39
Available-for-sale debt securities, Unrealized gains	1	0
Available-for-sale debt securities, Unrealized losses	0	0
Available-for-sale debt securities, Fair value	45	39
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	79	52
Available-for-sale debt securities, Unrealized gains	2	1
Available-for-sale debt securities, Unrealized losses	0	0
Available-for-sale debt securities, Fair value	$ 81	$ 53

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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