Investments in Marketable Securities - Summary of Investments in Marketable Securities (Details) - USD ($) $ in Millions	Jun. 30, 2019	Mar. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	$ 929	$ 629
Available-for-sale debt securities, Unrealized gains	19	8
Available-for-sale debt securities, Unrealized losses	(2)	(4)
Available-for-sale debt securities, Fair value	946	633
Equity investments, Fair value	2,350	2,275
Investments in marketable securities	3,296	2,908
U.S. government and agency obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	194	213
Available-for-sale debt securities, Unrealized gains	6	2
Available-for-sale debt securities, Unrealized losses	(1)	(3)
Available-for-sale debt securities, Fair value	199	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	325	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	325	50
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	100	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	100	70
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	163	160
Available-for-sale debt securities, Unrealized gains	8	3
Available-for-sale debt securities, Unrealized losses	(1)	(1)
Available-for-sale debt securities, Fair value	170	162
U.S. government agency mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	33	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	34	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	39	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	40	39
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	65	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	$ 66	$ 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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Amount, before tax, of unrealized loss 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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