Segment Information - Reportable Segments and Reconciliation to Consolidated Net Income (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018 USD ($) segment	Mar. 31, 2017 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)
Segment Reporting [Abstract]
Number of operating segments | segment	3
Segment Reporting Disclosure [Line Items]
Net sales	$ 51,042	$ 35,714
Operating expenses	49,115	34,709
Operating income (loss)	1,927	1,005
Total non-operating income (expense)	(11)	(52)
Provision for income taxes	(287)	(229)
Net income	1,629	724	$ 3,938	$ 2,583
North America
Segment Reporting Disclosure [Line Items]
Net sales	30,725	20,992
Operating expenses	29,576	20,396
Operating income (loss)	1,149	596
International
Segment Reporting Disclosure [Line Items]
Net sales	14,875	11,061
Operating expenses	15,497	11,542
Operating income (loss)	(622)	(481)
AWS
Segment Reporting Disclosure [Line Items]
Net sales	5,442	3,661
Operating expenses	4,042	2,771
Operating income (loss)	$ 1,400	$ 890