CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (UNAUDITED) - USD ($) shares in Millions, $ in Millions		Total	Conversion Of Series A Preferred Stock Upon Sale Into Public Market	Cumulative Effect, Period of Adoption, Adjustment	Series B preferred stock	Series C preferred stock	Class A common stock	Preferred Stock	Preferred Stock Conversion Of Series A Preferred Stock Upon Sale Into Public Market	Preferred Stock Series A preferred stock	[1]	Preferred Stock Series A preferred stock Conversion Of Series A Preferred Stock Upon Sale Into Public Market	[1]	Preferred Stock Series B preferred stock	Preferred Stock Series C preferred stock	Common Stock Class A common stock	Common Stock Class A common stock Conversion Of Series A Preferred Stock Upon Sale Into Public Market	Common Stock Class A common stock Conversion Of Class C Common Stock Upon Sale Into Public Market	Common Stock Class B common stock	Common Stock Class C common stock	Common Stock Class C common stock Conversion Of Class C Common Stock Upon Sale Into Public Market		Right to Recover for Covered Losses	Additional Paid-In Capital	Additional Paid-In Capital Conversion Of Series A Preferred Stock Upon Sale Into Public Market	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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of new accounting standards		$ 34,684		$ 0				$ 5,462															$ (171)	$ 16,541		$ 13,502	$ 25	$ (650)	$ (25)
Beginning balance (in shares) at Sep. 30, 2019														2	3	1,718			245	11
Beginning balance at Sep. 30, 2019		34,684		0				5,462															(171)	16,541		13,502	25	(650)	$ (25)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		8,729																								8,729
Other comprehensive income (loss), net of tax		396																										396
Comprehensive income		9,125
VE territory covered losses incurred		(22)																					(22)
Recovery through conversion rate adjustment		5			$ 72	$ 92		(164)															169
Conversion of stock (in shares)																		3			0	[1]
Vesting of restricted stock and performance-based shares (in shares)																3
Share-based compensation, net of forfeitures		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 class A 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 (in shares)							(37)									(37)
Repurchase of class A common stock		(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															(24)	16,457		14,072		(279)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of new accounting standards		34,585						5,462															(184)	16,385		13,366		(444)
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		(9)																					(9)
Recovery through conversion rate adjustment		5						(164)															169
Vesting of restricted stock and performance-based shares (in shares)	[1]															0
Share-based compensation, net of forfeitures		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 class A 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 (in shares)							(6)									(6)
Repurchase of class A common stock		(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															(24)	16,457		14,072		(279)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of new accounting standards		35,524						5,298															(24)	16,457		14,072		(279)
Adoption of new accounting standards		36,210		3				5,086						$ 1,106	$ 1,543								(39)	16,721		14,088	3	354
Beginning balance (in shares) at Sep. 30, 2020										0				2	3	1,683			245	11
Beginning balance at Sep. 30, 2020		36,210		$ 3				5,086						$ 1,106	$ 1,543								(39)	16,721		14,088	$ 3	354
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		8,727																								8,727
Other comprehensive income (loss), net of tax		247																										247
Comprehensive income		8,974
VE territory covered losses incurred		(38)												0	0								(38)
Recovery through conversion rate adjustment		(2)			$ 35	$ 20		(55)						$ (35)	$ (20)								53
Conversion of stock (in shares)												0					28	2			(1)
Conversion of stock			$ 0						$ (1,899)																$ 1,899
Vesting of restricted stock and performance-based shares (in shares)																3
Share-based compensation, net of forfeitures		434																						434
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		(142)																						(142)
Cash proceeds from issuance of common stock under employee equity plans (in shares)																1
Cash proceeds from issuance of class A common stock under employee equity plans		162																						162
Cash dividends declared and paid, at a quarterly amount per Class A share		(2,102)																								(2,102)
Repurchase of class A common stock (in shares)							(27)									(27)
Repurchase of class A common stock		(5,709)					$ (5,709)																	(287)		(5,422)
Ending balance (in shares) at Jun. 30, 2021										0				2	3	1,689			245	10
Ending balance at Jun. 30, 2021		37,790						3,132						$ 1,071	$ 1,523								(24)	18,787		15,294		601
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of new accounting standards		37,696						3,347															(41)	18,505		15,513		372
Beginning balance (in shares) at Mar. 31, 2021										0				2	3	1,694			245	11
Beginning balance at Mar. 31, 2021		37,696						3,347															(41)	18,505		15,513		372
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		2,575																								2,575
Other comprehensive income (loss), net of tax		229																										229
Comprehensive income		2,804
VE territory covered losses incurred		(21)																					(21)
Recovery through conversion rate adjustment		(2)						(40)															38
Conversion of stock (in shares)												0					3	2			(1)
Conversion of stock			$ 0						$ (175)																$ 175
Vesting of restricted stock and performance-based shares (in shares)	[1]															0
Share-based compensation, net of forfeitures		159																						159
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		(2)																						(2)
Cash proceeds from issuance of common stock under employee equity plans (in shares)	[1]															0
Cash proceeds from issuance of class A common stock under employee equity plans		54																						54
Cash dividends declared and paid, at a quarterly amount per Class A share		(698)																								(698)
Repurchase of class A common stock (in shares)							(10)									(10)
Repurchase of class A common stock		(2,200)					$ (2,200)																	(104)		(2,096)
Ending balance (in shares) at Jun. 30, 2021										0				2	3	1,689			245	10
Ending balance at Jun. 30, 2021		37,790						3,132						$ 1,071	$ 1,523								(24)	18,787		15,294		601
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of new accounting standards		$ 37,790						$ 3,132						$ 1,071	$ 1,523								$ (24)	$ 18,787		$ 15,294		$ 601

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