CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) shares in Millions, $ in Millions		Total	Series B Preferred Stock	Series C Preferred Stock	Class A common stock	Preferred Stock	Preferred Stock Series B Preferred Stock		Preferred Stock Series C Preferred Stock		Common Stock Class A common stock	Common Stock Class B common stock	Common Stock Class C common stock	Treasury Stock	Right to Recover for Covered Losses	Additional Paid-In Capital	Accumulated Income	Accumulated Other Comprehensive Income (Loss), Net
Beginning Balance (in shares) at Sep. 30, 2016							2	[1]	3	[1]	1,871	245	17
Beginning Balance at Sep. 30, 2016		$ 32,912				$ 5,717								$ (170)	$ (34)	$ 17,395	$ 10,462	$ (458)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		6,699															6,699
Other comprehensive income (loss), net of tax		1,336																1,336
Comprehensive income		8,035
VE territory covered losses incurred (Note 5)		(209)													(209)
Recovery through conversion rate adjustment (Note 5 and Note 14)			$ 190	$ 1		(191)									191
Charitable contribution of Visa Inc. shares (Note 14) (in shares)											2
Charitable contribution of Visa Inc. shares		170												170
Treasury stock appreciation, net of tax		14														14
Conversion of class C common stock upon sale into public market (in shares)											17		(4)
Vesting of restricted stock and performance-based shares (in shares)											2
Share-based compensation, net of forfeitures (Note 16) (in shares)	[2]										0
Share-based compensation, net of forfeitures (Note 16)		235														235
Restricted stock and performance-based shares settled in cash for taxes (in shares)											(1)
Restricted stock and performance-based shares settled in cash for taxes		(76)														(76)
Cash proceeds from issuance of common stock under employee equity plans (in shares)											4
Cash proceeds from issuance of common stock under employee equity plans		149														149
Cash dividends declared and paid, at a quarterly amount per Class A share		(1,579)															(1,579)
Repurchase of class A common stock (Note 13) (in shares)					(77)						(77)
Repurchase of class A common stock (Note 13)		(6,891)			$ (6,891)											(817)	(6,074)
Ending Balance (in shares) at Sep. 30, 2017							2	[3]	3	[3]	1,818	245	13
Ending Balance at Sep. 30, 2017		32,760				5,526								$ 0	(52)	16,900	9,508	878
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		10,301															10,301
Other comprehensive income (loss), net of tax		(331)																(331)
Comprehensive income		9,970
VE territory covered losses incurred (Note 5)		(11)													(11)
Recovery through conversion rate adjustment (Note 5 and Note 14)			35	21		(56)									56
Conversion of class C common stock upon sale into public market (in shares)											4		(1)
Vesting of restricted stock and performance-based shares (in shares)											2
Share-based compensation, net of forfeitures (Note 16) (in shares)	[4]										0
Share-based compensation, net of forfeitures (Note 16)		327														327
Restricted stock and performance-based shares settled in cash for taxes (in shares)											(1)
Restricted stock and performance-based shares settled in cash for taxes		(94)														(94)
Cash proceeds from issuance of common stock under employee equity plans (in shares)											3
Cash proceeds from issuance of common stock under employee equity plans		164														164
Cash dividends declared and paid, at a quarterly amount per Class A share		(1,918)															(1,918)
Repurchase of class A common stock (Note 13) (in shares)					(58)						(58)
Repurchase of class A common stock (Note 13)		(7,192)			$ (7,192)											(619)	(6,573)
Ending Balance (in shares) at Sep. 30, 2018							2	[3]	3	[3]	1,768	245	12
Ending Balance at Sep. 30, 2018		34,006				5,470	$ 2,291		$ 3,179						(7)	16,678	11,318	547
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		12,080															12,080
Other comprehensive income (loss), net of tax		(1,204)																(1,204)
Comprehensive income		10,876
Adoption of new accounting standards (Note 1)		392															385	7
VE territory covered losses incurred (Note 5)		(172)													(172)
Recovery through conversion rate adjustment (Note 5 and Note 14)		8	$ 6	$ 2		(8)	$ 6		$ 2						8
Conversion of class C common stock upon sale into public market (in shares)											2		(1)
Vesting of restricted stock and performance-based shares (in shares)											3
Share-based compensation, net of forfeitures (Note 16) (in shares)
Share-based compensation, net of forfeitures (Note 16)		407														407
Restricted stock and performance-based shares settled in cash for taxes (in shares)											(1)
Restricted stock and performance-based shares settled in cash for taxes		(111)														(111)
Cash proceeds from issuance of common stock under employee equity plans (in shares)											2
Cash proceeds from issuance of common stock under employee equity plans		162														162
Cash dividends declared and paid, at a quarterly amount per Class A share		(2,269)															(2,269)
Repurchase of class A common stock (Note 13) (in shares)					(56)						(56)
Repurchase of class A common stock (Note 13)		(8,607)			$ (8,607)											(595)	(8,012)
Ending Balance (in shares) at Sep. 30, 2019							2	[3]	3	[3]	1,718	245	11
Ending Balance at Sep. 30, 2019		$ 34,684				$ 5,462	$ 2,285		$ 3,177						$ (171)	$ 16,541	$ 13,502	$ (650)

[1] Series B and C preferred stock are alternatively referred to as UK&I and Europe preferred stock, respectively.

[2] Decrease in Class A common stock related to forfeitures of restricted stock awards is less than one million shares.

[3] Series B and C preferred stock are alternatively referred to as UK&I and Europe preferred stock, respectively.

[4] Decrease in Class A common stock related to forfeitures of restricted stock awards is less than one million shares.