Summary of Significant Accounting Policies (Details) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2017 USD ($) country	Mar. 31, 2016 USD ($)	Mar. 31, 2017 USD ($) country	Mar. 31, 2016 USD ($)
New Accounting Pronouncement, Early Adoption [Line Items]
Number of countries in which entity operates (more than) | country	200		200
Income tax provision (Note 12)	$ 2,272	$ 734	$ 3,181	$ 1,432
Increase to net cash provided by operating activities			2,904	2,819
Increase in net cash used in financing activities			(4,243)	$ 11,452
New Accounting Pronouncement, Early Adoption, Effect
New Accounting Pronouncement, Early Adoption [Line Items]
Income tax provision (Note 12)	$ (20)		(46)
Increase to net cash provided by operating activities			(46)
Increase in net cash used in financing activities			$ (46)