CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) shares in Millions, $ in Millions		Total	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 Other Comprehensive Income (Loss), Net
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		2,977											2,977
Other comprehensive income (loss), net of tax		(279)												(279)
Comprehensive income		2,698
Adoption of new accounting standards (Note 1)		400											393	7
VE territory covered losses incurred (Note 4)		(91)									(91)
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		0
Vesting of restricted stock and performance-based shares (in shares)							3
Share-based compensation, net of forfeitures (Note 11)		100										100
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		(101)										(101)
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		48										48
Cash dividends declared and paid, at a quarterly amount per Class A share		(572)											(572)
Repurchase of class A common stock (Note 10) (in shares)			(17)				(17)
Repurchase of class A common stock (Note 9)		(2,393)	$ (2,393)									(185)	(2,208)
Ending balance (in shares) at Dec. 31, 2018					2	3	1,754	245	12
Ending balance at Dec. 31, 2018		34,095		5,464							(92)	16,540	11,908	275
Beginning balance (in shares) at Sep. 30, 2019					2	3	1,718	245	11
Beginning balance at Sep. 30, 2019		34,684		5,462							(171)	16,541	13,502	(650)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		3,272											3,272
Other comprehensive income (loss), net of tax		335												335
Comprehensive income		3,607
Adoption of new accounting standards (Note 1)		0											25	(25)
VE territory covered losses incurred (Note 4)		(4)									(4)
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)							3
Share-based compensation, net of forfeitures (Note 11)		116										116
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		(147)										(147)
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		55										55
Cash dividends declared and paid, at a quarterly amount per Class A share		(671)											(671)
Repurchase of class A common stock (Note 10) (in shares)			(13)				(13)
Repurchase of class A common stock (Note 9)		(2,370)	$ (2,370)									(141)	(2,229)
Ending balance (in shares) at Dec. 31, 2019					2	3	1,709	245	11
Ending balance at Dec. 31, 2019		$ 35,270		$ 5,462							$ (175)	$ 16,424	$ 13,899	$ (340)

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

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