Restructuring Costs - Restructuring Liability (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Mar. 31, 2020
Restructuring Reserve [Roll Forward]
Costs Expensed, Net of Reversals	$ 104	$ 74	$ 441	$ 248
Restructuring Liability, ending balance	321		321
Fiscal 2021 Plan
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			0
Costs Expensed, Net of Reversals			441
Costs Not Affecting Restructuring Liability			(18)
Cash Paid			(221)
Other			8
Restructuring Liability, ending balance	210		210		$ 0
Fiscal 2021 Plan | Workforce Reductions
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			0
Costs Expensed, Net of Reversals			416
Costs Not Affecting Restructuring Liability			(9)
Cash Paid			(210)
Other			9
Restructuring Liability, ending balance	206		206		0
Fiscal 2021 Plan | Facilities Costs
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			0
Costs Expensed, Net of Reversals			25
Costs Not Affecting Restructuring Liability			(9)
Cash Paid			(11)
Other			(1)
Restructuring Liability, ending balance	4		4		0
Fiscal 2020 Plan
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			76
Costs Expensed, Net of Reversals			3
Costs Not Affecting Restructuring Liability			6
Cash Paid			(51)
Other			5
Restructuring Liability, ending balance	39		39		76
Costs expensed, net of reversals			11
Fiscal 2020 Plan | Workforce Reductions
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			74
Costs Expensed, Net of Reversals			7
Costs Not Affecting Restructuring Liability			2
Cash Paid			(49)
Other			5
Restructuring Liability, ending balance	39		39		74
Costs expensed, net of reversals					14
Fiscal 2020 Plan | Facilities Costs
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			2
Costs Expensed, Net of Reversals			(4)
Costs Not Affecting Restructuring Liability			4
Cash Paid			(2)
Other			0
Restructuring Liability, ending balance	0		0		2
Fiscal 2019 Plan
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			30
Costs Expensed, Net of Reversals			(5)
Costs Not Affecting Restructuring Liability			(1)
Cash Paid			(13)
Other			3
Restructuring Liability, ending balance	14		14		30
Costs expensed, net of reversals			10
Fiscal 2019 Plan | Workforce Reductions
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			25
Costs Expensed, Net of Reversals			(2)
Costs Not Affecting Restructuring Liability			(3)
Cash Paid			(13)
Other			2
Restructuring Liability, ending balance	9		9		25
Fiscal 2019 Plan | Facilities Costs
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			5
Costs Expensed, Net of Reversals			(3)
Costs Not Affecting Restructuring Liability			2
Cash Paid			0
Other			1
Restructuring Liability, ending balance	5		5		5
Other Prior Year Plans
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			24
Costs Expensed, Net of Reversals			1
Costs Not Affecting Restructuring Liability			2
Cash Paid			(14)
Other			2
Restructuring Liability, ending balance	15		15		24
Costs expensed, net of reversals			3
Other Prior Year Plans | Workforce Reductions
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			24
Costs Expensed, Net of Reversals			1
Costs Not Affecting Restructuring Liability			2
Cash Paid			(14)
Other			2
Restructuring Liability, ending balance	15		15		24
Other Prior Year Plans | 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		0
Acquired Liabilities
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			50
Costs Expensed, Net of Reversals			1
Costs Not Affecting Restructuring Liability			1
Cash Paid			(10)
Other			1
Restructuring Liability, ending balance	43		43		50
Acquired Liabilities | Workforce Reductions
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			39
Costs Expensed, Net of Reversals			1
Costs Not Affecting Restructuring Liability			0
Cash Paid			(7)
Other			1
Restructuring Liability, ending balance	34		34		39
Acquired Liabilities | Facilities Costs
Restructuring Reserve [Roll Forward]
Restructuring Liability, beginning balance			11
Costs Expensed, Net of Reversals			0
Costs Not Affecting Restructuring Liability			1
Cash Paid			(3)
Other			0
Restructuring Liability, ending balance	$ 9		$ 9		$ 11