CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (UNAUDITED) - USD ($) shares in Millions, $ in Millions		Total	Cumulative Effect, Period of Adoption, Adjustment	UK&I preferred stock	Europe preferred stock	Class A common stock	Preferred Stock	Preferred Stock UK&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 Income Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (Loss), Net	Accumulated Other Comprehensive Income (Loss), Net Cumulative Effect, Period of Adoption, Adjustment
Beginning balance (in shares) at Sep. 30, 2018								2	3	1,768	245	12
Beginning balance at Sep. 30, 2018		$ 34,006	$ 392				$ 5,470							$ (7)	$ 16,678	$ 11,318		$ 547
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		9,055														9,055
Other comprehensive income (loss), net of tax		(444)																(444)
Comprehensive income		8,611
VE territory covered losses incurred (Note 5)		(170)												(170)
Recovery through conversion rate adjustment (Note 5 and 10)				$ 6	$ 2		(8)							8
Conversion of class C common stock upon sales into public market (in shares)										1		0	[1]
Vesting of restricted stock and performance-based shares (in shares)										3
Share-based compensation, net of forfeitures (Note 12)		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 10) (in shares)						(44)				(44)
Repurchase of class A common stock (Note 10)		(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	$ 385	110	$ 7
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														3,101
Other comprehensive income (loss), net of tax		196																196
Comprehensive income		3,297
VE territory covered losses incurred (Note 5)		(8)												(8)
Recovery through conversion rate adjustment (Note 5 and 10)		0					(2)							2
Conversion of class C common stock upon sales into public market (in shares)	[1]									0		0
Vesting of restricted stock and performance-based shares (in shares)	[1]									0
Share-based compensation, net of forfeitures (Note 12)		110													110
Restricted stock and performance-based shares settled in cash for taxes (in shares)	[1]									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)										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 10) (in shares)						(13)				(13)
Repurchase of class A common stock (Note 10)		(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	385	110	7
Beginning balance (in shares) at Sep. 30, 2019								2	3	1,718	245	11
Beginning balance at Sep. 30, 2019		34,684					5,462	$ 2,285	$ 3,177					(171)	16,541	13,502		(650)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		8,729														8,729
Other comprehensive income (loss), net of tax		396
Comprehensive income		9,125
VE territory covered losses incurred (Note 5)		(22)						0	0					(22)
Recovery through conversion rate adjustment (Note 5 and 10)		5		$ 72	$ 92		(164)	$ 72	$ 92					169
Conversion of class C common stock upon sales into public market (in shares)										3		0	[1]
Vesting of restricted stock and performance-based shares (in shares)										3
Share-based compensation, net of forfeitures (Note 12)		322													322
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		(158)													(158)
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		142													142
Cash dividends declared and paid, at a quarterly amount per Class A share		(2,002)														(2,002)
Repurchase of class A common stock (Note 10) (in shares)						(37)				(37)
Repurchase of class A common stock (Note 10)		(6,572)				$ (6,572)									(390)	(6,182)
Ending balance (in shares) at Jun. 30, 2020								2	3	1,687	245	11
Ending balance at Jun. 30, 2020		35,524					5,298	$ 2,213	$ 3,085					(24)	16,457	14,072	25	(279)	(25)
Beginning balance (in shares) at Mar. 31, 2020								2	3	1,693	245	11
Beginning balance at Mar. 31, 2020		34,585					5,462							(184)	16,385	13,366		(444)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		2,373														2,373
Other comprehensive income (loss), net of tax		165																165
Comprehensive income		2,538
VE territory covered losses incurred (Note 5)		(9)												(9)
Recovery through conversion rate adjustment (Note 5 and 10)		5					(164)							169
Vesting of restricted stock and performance-based shares (in shares)	[1]									0
Share-based compensation, net of forfeitures (Note 12)		107													107
Restricted stock and performance-based shares settled in cash for taxes (in shares)	[1]									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)	[1]									0
Cash proceeds from issuance of common stock under employee equity plans		33													33
Cash dividends declared and paid, at a quarterly amount per Class A share		(663)														(663)
Repurchase of class A common stock (Note 10) (in shares)						(6)				(6)
Repurchase of class A common stock (Note 10)		(1,069)				$ (1,069)									(65)	(1,004)
Ending balance (in shares) at Jun. 30, 2020								2	3	1,687	245	11
Ending balance at Jun. 30, 2020		$ 35,524					$ 5,298	$ 2,213	$ 3,085					$ (24)	$ 16,457	$ 14,072	$ 25	$ (279)	$ (25)

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