CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016		Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 6,699	$ 5,991	[1]	$ 6,328
Investment securities, available-for-sale:
Net unrealized gain (loss)	60	51		(21)
Income tax effect	(24)	(18)		8
Reclassification adjustment for net loss (gain) realized in net income	1	(3)		(21)
Income tax effect	0	1		8
Defined benefit pension and other postretirement plans:
Net unrealized actuarial gain (loss) and prior service credit	183	(106)		(122)
Income tax effect	(54)	36		45
Amortization of actuarial loss (gain) and prior service credit realized in net income	32	10		(1)
Income tax effect	(12)	(4)		1
Derivative instruments classified as cash flow hedges:
Net unrealized (loss) gain	(22)	(74)		172
Income tax effect	15	9		(51)
Reclassification adjustment for net loss (gain) realized in net income	33	(103)		(102)
Income tax effect	(12)	35		26
Foreign currency translation adjustments	1,136	(218)		1
Other comprehensive income (loss), net of tax	1,336	(384)		(57)
Comprehensive income	$ 8,035	$ 5,607		$ 6,271

[1] See Note 2—Visa Europe.