Restructuring Costs - Restructuring Liability (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Restructuring Reserve [Roll Forward]
Costs Expensed, net of reversals	$ 32	$ 157	$ 174	$ 342
Restructuring Liability, ending balance	239		239
Fiscal 2020 Plan
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			0
Adoption of ASC 842			0
Costs Expensed, net of reversals			198
Costs Not Affecting Restructuring Liability			(15)
Cash Paid			(106)
Other			(4)
Restructuring Liability, ending balance	73		73
Fiscal 2020 Plan | Workforce Reductions
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			0
Adoption of ASC 842			0
Costs Expensed, net of reversals			182
Costs Not Affecting Restructuring Liability			(7)
Cash Paid			(100)
Other			(4)
Restructuring Liability, ending balance	71		71
Fiscal 2020 Plan | Facilities Costs
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			0
Adoption of ASC 842			0
Costs Expensed, net of reversals			16
Costs Not Affecting Restructuring Liability			(8)
Cash Paid			(6)
Other			0
Restructuring Liability, ending balance	2		2
Fiscal 2019 Plan
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			206
Adoption of ASC 842			(53)
Costs Expensed, net of reversals			(10)
Costs Not Affecting Restructuring Liability			(6)
Cash Paid			(66)
Other			(3)
Restructuring Liability, ending balance	68		68
Costs reversed			14
Fiscal 2019 Plan | Workforce Reductions
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			138
Adoption of ASC 842			0
Costs Expensed, net of reversals			(10)
Costs Not Affecting Restructuring Liability			(5)
Cash Paid			(59)
Other			(3)
Restructuring Liability, ending balance	61		61
Fiscal 2019 Plan | Facilities Costs
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			68
Adoption of ASC 842			(53)
Costs Expensed, net of reversals			0
Costs Not Affecting Restructuring Liability			(1)
Cash Paid			(7)
Other			0
Restructuring Liability, ending balance	7		7
Fiscal 2018 Plan
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			94
Adoption of ASC 842			(36)
Costs Expensed, net of reversals			(10)
Costs Not Affecting Restructuring Liability			0
Cash Paid			(19)
Other			4
Restructuring Liability, ending balance	33		33
Costs reversed			10
Fiscal 2018 Plan | Workforce Reductions
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			59
Adoption of ASC 842			0
Costs Expensed, net of reversals			(9)
Costs Not Affecting Restructuring Liability			0
Cash Paid			(17)
Other			0
Restructuring Liability, ending balance	33		33
Fiscal 2018 Plan | Facilities Costs
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			35
Adoption of ASC 842			(36)
Costs Expensed, net of reversals			(1)
Costs Not Affecting Restructuring Liability			0
Cash Paid			(2)
Other			4
Restructuring Liability, ending balance	0		0
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			0
Other			0
Restructuring Liability, ending balance	8		8
Costs reversed			1
Other Prior Year Plans | Workforce Reductions
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			0
Other			0
Restructuring Liability, ending balance	8		8
Other Prior Year Plans | Facilities Costs
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		0
Acquired Liabilities
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			69
Adoption of ASC 842			0
Costs Expensed, net of reversals			(3)
Costs Not Affecting Restructuring Liability			0
Cash Paid			(6)
Other			(3)
Restructuring Liability, ending balance	57		57
Acquired Liabilities | Workforce Reductions
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			51
Adoption of ASC 842			0
Costs Expensed, net of reversals			1
Costs Not Affecting Restructuring Liability			0
Cash Paid			(5)
Other			0
Restructuring Liability, ending balance	47		47
Acquired Liabilities | Facilities Costs
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			18
Adoption of ASC 842			0
Costs Expensed, net of reversals			(4)
Costs Not Affecting Restructuring Liability			0
Cash Paid			(1)
Other			(3)
Restructuring Liability, ending balance	$ 10		$ 10