Summary of Significant Accounting Policies - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Apr. 01, 2017	Mar. 31, 2018	Apr. 01, 2017
Numerator:
Net income	$ 13,822	$ 11,029	$ 33,887	$ 28,920
Denominator:
Weighted-average basic shares outstanding (in shares)	5,024,877	5,225,791	5,068,877	5,262,226
Effect of dilutive securities (in shares)	43,616	35,897	44,263	32,615
Weighted-average diluted shares (in shares)	5,068,493	5,261,688	5,113,140	5,294,841
Basic earnings per share (in dollars per share)	$ 2.75	$ 2.11	$ 6.69	$ 5.50
Diluted earnings per share (in dollars per share)	$ 2.73	$ 2.10	$ 6.63	$ 5.46