CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) shares in Millions, $ in Millions		Total	U.K.& I preferred stock	Europe preferred stock	Class A common stock	Preferred Stock	Preferred Stock U.K.& I preferred stock	Preferred Stock Europe preferred stock	Common Stock Class A common stock	Common Stock Class B common stock	Common Stock Class C common stock		Right to Recover for Covered Losses	Additional Paid-in Capital	Accumulated Income	Accumulated Other Comprehensive Income
Beginning balance (in shares) at Sep. 30, 2017							2	3	1,818	245	13
Beginning balance at Sep. 30, 2017		$ 32,760				$ 5,526							$ (52)	$ 16,900	$ 9,508	$ 878
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		7,456
Other comprehensive income (loss), net of tax		(137)														(137)
Comprehensive income		7,319
VE territory covered losses incurred (Note 4)		(9)											(9)
Recovery through conversion rate adjustment (Note 4 and Note 9)						(56)							56
Conversion of class C common stock upon sales into public market (in shares)									3		(1)
Vesting of restricted stock and performance-based shares (in shares)									2
Share-based compensation, net of forfeitures (Note11) (in shares)	[1]								0
Share-based compensation, net of forfeitures (Note11)		242												242
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		(90)												(90)
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		135												135
Cash dividends declared and paid, at a quarterly amount per Class A share		(1,435)													(1,435)
Repurchase of class A common stock (Note 9) (in shares)					(47)				(47)
Repurchase of class A common stock (Note 9)		(5,604)			$ (5,604)									(501)	(5,103)
Ending balance (in shares) at Jun. 30, 2018							2	3	1,778	245	12
Ending balance at Jun. 30, 2018		33,318				5,470							(5)	16,686	10,426	741
Beginning balance (in shares) at Sep. 30, 2017							2	3	1,818	245	13
Beginning balance at Sep. 30, 2017		32,760				5,526							(52)	16,900	9,508	878
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Recovery through conversion rate adjustment (Note 4 and Note 9)			$ 35	$ 21
Ending balance (in shares) at Sep. 30, 2018							2	3	1,768	245	12
Ending balance at Sep. 30, 2018		34,006				5,470							(7)	16,678	11,318	547
Beginning balance (in shares) at Mar. 31, 2018							2	3	1,790	245	12
Beginning balance at Mar. 31, 2018		34,103				5,476							(6)	16,713	10,192	1,728
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		2,329
Other comprehensive income (loss), net of tax		(987)														(987)
Comprehensive income		1,342
VE territory covered losses incurred (Note 4)		(5)											(5)
Recovery through conversion rate adjustment (Note 4 and Note 9)						(6)							6
Conversion of class C common stock upon sales into public market (in shares)									1		0	[2]
Vesting of restricted stock and performance-based shares (in shares)	[2]								0
Share-based compensation, net of forfeitures (Note11) (in shares)	[2]								0
Share-based compensation, net of forfeitures (Note11)		89												89
Restricted stock and performance-based shares settled in cash for taxes (in shares)	[2]								0
Restricted stock and performance-based shares settled in cash for taxes		(2)												(2)
Cash proceeds from issuance of common stock under employee equity plans (in shares)									1
Cash proceeds from issuance of common stock under employee equity plans		32												32
Cash dividends declared and paid, at a quarterly amount per Class A share		(487)													(487)
Repurchase of class A common stock (Note 9) (in shares)					(14)				(14)
Repurchase of class A common stock (Note 9)		(1,754)			$ (1,754)									(146)	(1,608)
Ending balance (in shares) at Jun. 30, 2018							2	3	1,778	245	12
Ending balance at Jun. 30, 2018		33,318				5,470							(5)	16,686	10,426	741
Beginning balance (in shares) at Sep. 30, 2018							2	3	1,768	245	12
Beginning balance at Sep. 30, 2018		34,006				5,470							(7)	16,678	11,318	547
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		9,055
Other comprehensive income (loss), net of tax		(444)														(444)
Comprehensive income		8,611
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification		392													385	7
VE territory covered losses incurred (Note 4)		(170)	0	0									(170)
Recovery through conversion rate adjustment (Note 4 and Note 9)			$ 6	$ 2		(8)							8
Conversion of class C common stock upon sales into public market (in shares)									1		0	[3]
Vesting of restricted stock and performance-based shares (in shares)									3
Share-based compensation, net of forfeitures (Note11)		321												321
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		(106)												(106)
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		127												127
Cash dividends declared and paid, at a quarterly amount per Class A share		(1,706)													(1,706)
Repurchase of class A common stock (Note 9) (in shares)					(44)				(44)
Repurchase of class A common stock (Note 9)		(6,480)			$ (6,480)									(468)	(6,012)
Ending balance (in shares) at Jun. 30, 2019							2	3	1,729	245	12
Ending balance at Jun. 30, 2019		34,995				5,462							(169)	16,552	13,040	110
Beginning balance (in shares) at Mar. 31, 2019							2	3	1,741	245	12
Beginning balance at Mar. 31, 2019		34,275				5,464							(163)	16,547	12,513	(86)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		3,101
Other comprehensive income (loss), net of tax		196														196
Comprehensive income		3,297
VE territory covered losses incurred (Note 4)		(8)											(8)
Recovery through conversion rate adjustment (Note 4 and Note 9)						(2)							2
Conversion of class C common stock upon sales into public market (in shares)									0		0	[4]
Vesting of restricted stock and performance-based shares (in shares)	[4]								0
Share-based compensation, net of forfeitures (Note11)		110												110
Restricted stock and performance-based shares settled in cash for taxes (in shares)	[4]								0
Restricted stock and performance-based shares settled in cash for taxes		(3)												(3)
Cash proceeds from issuance of common stock under employee equity plans (in shares)	[4]								1
Cash proceeds from issuance of common stock under employee equity plans		38												38
Cash dividends declared and paid, at a quarterly amount per Class A share		(565)													(565)
Repurchase of class A common stock (Note 9) (in shares)					(13)				(13)
Repurchase of class A common stock (Note 9)		(2,149)			$ (2,149)									(140)	(2,009)
Ending balance (in shares) at Jun. 30, 2019							2	3	1,729	245	12
Ending balance at Jun. 30, 2019		$ 34,995				$ 5,462							$ (169)	$ 16,552	$ 13,040	$ 110

[1] Decrease is less than one million shares.

[2] Increase or decrease is less than one million shares.

[3] Decrease is less than one million shares.

[4] Increase or decrease is less than one million shares.