Restructuring Costs - Restructuring Liability (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance	$ 379
Costs Expensed, Net of Reversals	252	$ 465	$ 789
Restructuring Liability, ending balance	180	379
Fiscal 2020 Plan
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance	0
Adoption of ASC 842	0
Costs Expensed, Net of Reversals	292
Costs Not Affecting Restructuring Liability	(14)
Cash Paid	(193)
Other	(9)
Restructuring Liability, ending balance	76	0
Fiscal 2019 Plan
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance	206	0
Adoption of ASC 842	(53)
Costs Expensed, Net of Reversals	(25)	507
Costs Not Affecting Restructuring Liability	(1)	(8)
Cash Paid	(90)	(286)
Other	(7)	(7)
Restructuring Liability, ending balance	30	206	0
Costs reversed	30
Fiscal 2018 Plan
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance	94	355
Adoption of ASC 842	(36)
Costs Expensed, Net of Reversals	(11)	(44)
Costs Not Affecting Restructuring Liability	0	(3)
Cash Paid	(31)	(191)
Other	4	(23)
Restructuring Liability, ending balance	20	94	355
Costs reversed	11	48
Other Prior Year Plans
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance	10
Adoption of ASC 842	(1)
Costs Expensed, Net of Reversals	(1)
Costs Not Affecting Restructuring Liability	0
Cash Paid	(3)
Other	(1)
Restructuring Liability, ending balance	4	10
Costs reversed	3
Fiscal 2017 Plan
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance	7	22
Costs Expensed, Net of Reversals		0
Costs Not Affecting Restructuring Liability		0
Cash Paid		(15)
Other		0
Restructuring Liability, ending balance		7	22
Costs reversed		3
Other Prior Year Plans
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance	3	6
Costs Expensed, Net of Reversals		0
Costs Not Affecting Restructuring Liability		0
Cash Paid		(3)
Other		0
Restructuring Liability, ending balance		3	6
Costs reversed		1
Acquired Liabilities
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance	69	137
Adoption of ASC 842	0
Costs Expensed, Net of Reversals	(3)	2
Costs Not Affecting Restructuring Liability	0	0
Cash Paid	(17)	(67)
Other	1	(3)
Restructuring Liability, ending balance	50	69	137
Workforce Reductions | Fiscal 2020 Plan
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance	0
Adoption of ASC 842	0
Costs Expensed, Net of Reversals	271
Costs Not Affecting Restructuring Liability	(11)
Cash Paid	(177)
Other	(9)
Restructuring Liability, ending balance	74	0
Workforce Reductions | Fiscal 2019 Plan
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance	138	0
Adoption of ASC 842	0
Costs Expensed, Net of Reversals	(25)	363
Costs Not Affecting Restructuring Liability	0	(2)
Cash Paid	(83)	(218)
Other	(5)	(5)
Restructuring Liability, ending balance	25	138	0
Workforce Reductions | Fiscal 2018 Plan
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance	59	257
Adoption of ASC 842	0
Costs Expensed, Net of Reversals	(10)	(30)
Costs Not Affecting Restructuring Liability	0	0
Cash Paid	(29)	(151)
Other	0	(17)
Restructuring Liability, ending balance	20	59	257
Workforce Reductions | Other Prior Year Plans
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance	9
Adoption of ASC 842	0
Costs Expensed, Net of Reversals	(1)
Costs Not Affecting Restructuring Liability	0
Cash Paid	(3)
Other	(1)
Restructuring Liability, ending balance	4	9
Workforce Reductions | Fiscal 2017 Plan
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance	7	19
Costs Expensed, Net of Reversals		0
Costs Not Affecting Restructuring Liability		0
Cash Paid		(12)
Other		0
Restructuring Liability, ending balance		7	19
Workforce Reductions | Other Prior Year Plans
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance	2	4
Costs Expensed, Net of Reversals		0
Costs Not Affecting Restructuring Liability		0
Cash Paid		(2)
Other		0
Restructuring Liability, ending balance		2	4
Workforce Reductions | Acquired Liabilities
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance	51	110
Adoption of ASC 842	0
Costs Expensed, Net of Reversals	1	2
Costs Not Affecting Restructuring Liability	0	0
Cash Paid	(16)	(58)
Other	3	(3)
Restructuring Liability, ending balance	39	51	110
Facilities Costs | Fiscal 2020 Plan
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance	0
Adoption of ASC 842	0
Costs Expensed, Net of Reversals	21
Costs Not Affecting Restructuring Liability	(3)
Cash Paid	(16)
Other	0
Restructuring Liability, ending balance	2	0
Facilities Costs | Fiscal 2019 Plan
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance	68	0
Adoption of ASC 842	(53)
Costs Expensed, Net of Reversals	0	144
Costs Not Affecting Restructuring Liability	(1)	(6)
Cash Paid	(7)	(68)
Other	(2)	(2)
Restructuring Liability, ending balance	5	68	0
Facilities Costs | Fiscal 2018 Plan
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance	35	98
Adoption of ASC 842	(36)
Costs Expensed, Net of Reversals	(1)	(14)
Costs Not Affecting Restructuring Liability	0	(3)
Cash Paid	(2)	(40)
Other	4	(6)
Restructuring Liability, ending balance	0	35	98
Facilities Costs | Other Prior Year Plans
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance	1
Adoption of ASC 842	(1)
Costs Expensed, Net of Reversals	0
Costs Not Affecting Restructuring Liability	0
Cash Paid	0
Other	0
Restructuring Liability, ending balance	0	1
Facilities Costs | Fiscal 2017 Plan
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance	0	3
Costs Expensed, Net of Reversals		0
Costs Not Affecting Restructuring Liability		0
Cash Paid		(3)
Other		0
Restructuring Liability, ending balance		0	3
Facilities Costs | Other Prior Year Plans
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance	1	2
Costs Expensed, Net of Reversals		0
Costs Not Affecting Restructuring Liability		0
Cash Paid		(1)
Other		0
Restructuring Liability, ending balance		1	2
Facilities Costs | Acquired Liabilities
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance	18	27
Adoption of ASC 842	0
Costs Expensed, Net of Reversals	(4)	0
Costs Not Affecting Restructuring Liability	0	0
Cash Paid	(1)	(9)
Other	(2)	0
Restructuring Liability, ending balance	$ 11	$ 18	$ 27