Restructuring Costs - Restructuring Liability (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Restructuring Reserve [Roll Forward]
Costs Expensed, net of reversals	$ 192	$ 25	$ 382	$ 82
Restructuring Liability, ending balance	498		498
Fiscal 2018 Plan
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			0
Costs Expensed, net of reversals			406
Costs Not Affecting Restructuring Liability			(11)
Cash Paid			(195)
Other			4
Restructuring Liability, ending balance	204		204
Fiscal 2018 Plan | Workforce Reductions
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			0
Costs Expensed, net of reversals			282
Costs Not Affecting Restructuring Liability			0
Cash Paid			(153)
Other			1
Restructuring Liability, ending balance	130		130
Fiscal 2018 Plan | Facilities Costs
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			0
Costs Expensed, net of reversals			124
Costs Not Affecting Restructuring Liability			(11)
Cash Paid			(42)
Other			3
Restructuring Liability, ending balance	74		74
Fiscal 2017 Plan
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			161
Costs Expensed, net of reversals			(19)
Costs Not Affecting Restructuring Liability			0
Cash Paid			(77)
Other			1
Restructuring Liability, ending balance	66		66
Costs reversed			19
Fiscal 2017 Plan | Workforce Reductions
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			155
Costs Expensed, net of reversals			(17)
Costs Not Affecting Restructuring Liability			0
Cash Paid			(74)
Other			0
Restructuring Liability, ending balance	64		64
Fiscal 2017 Plan | Facilities Costs
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			6
Costs Expensed, net of reversals			(2)
Costs Not Affecting Restructuring Liability			0
Cash Paid			(3)
Other			1
Restructuring Liability, ending balance	2		2
Fiscal 2016 Plan
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			13
Costs Expensed, net of reversals			(1)
Costs Not Affecting Restructuring Liability			0
Cash Paid			(5)
Other			0
Restructuring Liability, ending balance	7		7
Costs reversed			1
Fiscal 2016 Plan | Workforce Reductions
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			8
Costs Expensed, net of reversals			(1)
Costs Not Affecting Restructuring Liability			0
Cash Paid			(2)
Other			0
Restructuring Liability, ending balance	5		5
Fiscal 2016 Plan | Facilities Costs
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			5
Costs Expensed, net of reversals			0
Costs Not Affecting Restructuring Liability			0
Cash Paid			(3)
Other			0
Restructuring Liability, ending balance	2		2
Fiscal 2015 Plan
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			3
Costs Expensed, net of reversals			0
Costs Not Affecting Restructuring Liability			0
Cash Paid			(1)
Other			0
Restructuring Liability, ending balance	2		2
Fiscal 2015 Plan | Workforce Reductions
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			3
Costs Expensed, net of reversals			0
Costs Not Affecting Restructuring Liability			0
Cash Paid			(1)
Other			0
Restructuring Liability, ending balance	2		2
Fiscal 2015 Plan | Facilities Costs
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			0
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			333
Costs Expensed, net of reversals			(4)
Costs Not Affecting Restructuring Liability			(2)
Cash Paid			(115)
Other			7
Restructuring Liability, ending balance	219		219
Costs reversed			4
Acquired Liabilities | Workforce Reductions
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			256
Costs Expensed, net of reversals			0
Costs Not Affecting Restructuring Liability			(2)
Cash Paid			(93)
Other			6
Restructuring Liability, ending balance	167		167
Acquired Liabilities | Facilities Costs
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			77
Costs Expensed, net of reversals			(4)
Costs Not Affecting Restructuring Liability			0
Cash Paid			(22)
Other			1
Restructuring Liability, ending balance	$ 52		$ 52