Cash and Cash Equivalents and Investments in Marketable Securities - Summary of Investments in Marketable Securities (Details) - USD ($) $ in Millions	12 Months Ended
Mar. 31, 2018	Mar. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost		$ 629
Available-for-sale debt securities, Unrealized gains		8
Available-for-sale debt securities, Unrealized losses		(4)
Available-for-sale debt securities, Fair value		633
Equity investments, Amortized cost	$ 2,196
Equity investments, Unrealized gains	11
Equity investments, Unrealized losses	(23)
Equity investments, Fair value	2,184	2,275
Total investments in marketable securities, Amortized cost	5,865
Total investments in marketable securities, Unrealized gain	15
Total investments in marketable securities, Unrealized losses	(51)
Investments in marketable securities	5,829	2,908
U.S. government and agency obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	2,821	213
Available-for-sale debt securities, Unrealized gains	0	2
Available-for-sale debt securities, Unrealized losses	(23)	(3)
Available-for-sale debt securities, Fair value	2,798	212
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	1	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	475	50
Available-for-sale debt securities, Unrealized gains	0	0
Available-for-sale debt securities, Unrealized losses	(1)	0
Available-for-sale debt securities, Fair value	474	50
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	52	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	52	70
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	203	160
Available-for-sale debt securities, Unrealized gains	1	3
Available-for-sale debt securities, Unrealized losses	(3)	(1)
Available-for-sale debt securities, Fair value	201	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	1	0
Available-for-sale debt securities, Unrealized losses	0	0
Available-for-sale debt securities, Fair value	2	1
Non-agency commercial mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	30	39
Available-for-sale debt securities, Unrealized gains	0	0
Available-for-sale debt securities, Unrealized losses	(1)	0
Available-for-sale debt securities, Fair value	29	39
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Amortized cost	39	52
Available-for-sale debt securities, Unrealized gains	0	1
Available-for-sale debt securities, Unrealized losses	0	0
Available-for-sale debt securities, Fair value	$ 39	$ 53

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