Investments in Marketable Securities - Summary of Investments in Marketable Securities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Mar. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	$ 1,199	$ 629
Available-for-sale debt securities, Unrealized gains	20	8
Available-for-sale debt securities, Unrealized losses	(1)	(4)
Available-for-sale debt securities, Fair value	1,218	633
Equity investments, Fair value	2,409	2,275
Investments in marketable securities total	3,627	2,908
U.S. government and agency obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	211	213
Available-for-sale debt securities, Unrealized gains	5	2
Available-for-sale debt securities, Unrealized losses	(1)	(3)
Available-for-sale debt securities, Fair value	215	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	315	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	315	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	147	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	157	162
U.S. government agency mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	38	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	39	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	48	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	49	39
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	80	52
Available-for-sale debt securities, Unrealized gains	1	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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