Income Taxes - Narrative (Details) - USD ($) $ in Millions		3 Months Ended				12 Months Ended
	Mar. 01, 2017	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Income Tax Contingency [Line Items]
Income tax expense (benefit)						$ 356	$ (53)	$ 1,614
Income tax rates (percent)						58.40%	(22.20%)	23.40%
Statutory federal income tax rate (percent)						21.00%	31.60%	35.00%
Research and development credit						$ 7	$ 11	$ 14
Non-cash pre-tax charge						1,797	1,738	290
Non-cash after-tax charge							1,738
Net discrete tax benefit			$ 42
Net tax benefit on intellectual property transfer						42	178	137
Tax expense recognized on gain from asset exchange	$ 929
Tax expense (benefit) related to adoption of amended accounting guidance						4	(8)	(54)
Valuation allowance		$ 870				870	751
Increase in valuation allowance						119
Unrecognized tax benefits		1,052				1,052	1,183	486	$ 555
Unrecognized tax benefits that would Impact income tax expense and the effective tax rate		877				877
Decrease in unrecognized tax benefits						171
Income tax expense (benefit), before any tax effect, related to accrued interest and penalties						33	(1)	(6)
Accrued interest and penalties on unrecognized tax benefits		68				68	37
Tax benefit resulting from favorable resolution of various uncertain tax positions					$ 39	13	7	113
Provisional net tax benefit							1,324
Tax benefit related to change in tax method for inventory						81
Transition tax on foreign earnings						(5)	457	0
Undistributed earnings of foreign operations		4,900				4,900
Federal
Income Tax Contingency [Line Items]
Federal, state and foreign net operating loss carryforwards		92				92
State
Income Tax Contingency [Line Items]
Federal, state and foreign net operating loss carryforwards		3,551				3,551
Foreign Tax Authority
Income Tax Contingency [Line Items]
Federal, state and foreign net operating loss carryforwards		2,143				2,143
Capital loss carryforwards		742				742
European Pharmaceutical Solutions
Income Tax Contingency [Line Items]
Non-cash pre-tax charge		$ 1,206		$ 570		1,776	1,283
Non-cash after-tax charge						1,756	$ 1,283
Technology Solutions
Income Tax Contingency [Line Items]
Non-cash pre-tax charge								290
Non-cash after-tax charge								$ 282
New Accounting Pronouncement, Early Adoption, Effect
Income Tax Contingency [Line Items]
Tax expense (benefit) related to adoption of amended accounting guidance						$ 4