CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - 3 months ended Dec. 31, 2018 - USD ($) shares in Millions, $ in Millions		Total	U.K.& I preferred stock	Europe preferred stock	Class A common stock	[3]	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, 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
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)		0	$ 5	$ 1			(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 of $0.25 per as-converted share (Note 9)		(572)													(572)
Repurchase of class A common stock (Note 9) (in shares)					(17)	[2]				(17)
Repurchase of class A common stock (Note 9)					$ (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

[1] Increase or decrease in conversion of class C common stock is less than one million shares.

[2] All shares repurchased in the open market have been retired and constitute authorized but unissued shares.

[3] Figures in the table may not recalculate exactly due to rounding. Shares repurchased in the open market reflect repurchases settled during the three months ended December 31, 2018 and 2017. These amounts include repurchases traded but not yet settled on or before September 30, 2018 and 2017, respectively, and exclude repurchases traded but not yet settled on or before December 31, 2018 and 2017, respectively.