Segment Information - Reportable Segments and Reconciliation to Consolidated Net Income (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019 USD ($) segment	Mar. 31, 2018 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)
Segment Reporting [Abstract]
Number of operating segments | segment	3
Segment Reporting Disclosure [Line Items]
Net sales	$ 59,700	$ 51,042
Operating expenses	55,280	49,115
Operating income (loss)	4,420	1,927
Total non-operating income (expense)	(19)	(11)
Provision for income taxes	(836)	(287)
Equity-method investment activity, net of tax	(4)	0
Net income	3,561	1,629	$ 12,005	$ 3,938
North America
Segment Reporting Disclosure [Line Items]
Net sales	35,812	30,725
Operating expenses	33,525	29,576
Operating income (loss)	2,287	1,149
International
Segment Reporting Disclosure [Line Items]
Net sales	16,192	14,875
Operating expenses	16,282	15,497
Operating income (loss)	(90)	(622)
AWS
Segment Reporting Disclosure [Line Items]
Net sales	7,696	5,442
Operating expenses	5,473	4,042
Operating income (loss)	$ 2,223	$ 1,400