CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (UNAUDITED) - USD ($) shares in Millions, $ in Millions		Total	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		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					$ 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					5,462																(171)	16,541		13,502	25	(650)	(25)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		6,356																								6,356
Other comprehensive income (loss), net of tax		231																										231
Comprehensive income		6,587
Adoption of new accounting standards		34,585					5,462																(171)	16,385		13,502	25	(444)	$ (25)
VE territory covered losses incurred		(13)																					(13)
Conversion of stock (in shares)																	(3)				0
Vesting of restricted stock and performance-based shares (in shares)															3
Share-based compensation, net of forfeitures		215																						215
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		(155)																						(155)
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		109																						109
Cash dividends declared and paid, at a quarterly amount per Class A share		(1,339)																								(1,339)
Repurchase of class A common stock (in shares)						(31)									(31)
Repurchase of class A common stock		(5,503)				$ (5,503)																		(325)		(5,178)
Ending balance (in shares) at Mar. 31, 2020													2	3	1,693				245	11
Ending balance at Mar. 31, 2020		34,585					5,462																(184)	16,385		13,366		(444)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of new accounting standards		35,270					5,462																(175)	16,424		13,899		(340)
Beginning balance (in shares) at Dec. 31, 2019													2	3	1,709				245	11
Beginning balance at Dec. 31, 2019		35,270					5,462																(175)	16,424		13,899		(340)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		3,084																								3,084
Other comprehensive income (loss), net of tax		(104)																										(104)
Comprehensive income		2,980
Adoption of new accounting standards		34,585					5,462																(184)	16,385		13,366		(444)
VE territory covered losses incurred		(9)																					(9)
Conversion of stock (in shares)																	(2)				0
Vesting of restricted stock and performance-based shares (in shares)															0
Share-based compensation, net of forfeitures		99																						99
Restricted stock and performance-based shares settled in cash for taxes (in shares)															0
Restricted stock and performance-based shares settled in cash for taxes		(8)																						(8)
Cash proceeds from issuance of common stock under employee equity plans (in shares)															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		(668)																								(668)
Repurchase of class A common stock (in shares)						(18)									(18)
Repurchase of class A common stock		(3,133)				$ (3,133)																		(184)		(2,949)
Ending balance (in shares) at Mar. 31, 2020													2	3	1,693				245	11
Ending balance at Mar. 31, 2020		34,585					5,462																(184)	16,385		13,366		(444)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of new accounting standards		34,585					5,462																(184)	16,385		13,366		(444)
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		6,152																								6,152
Other comprehensive income (loss), net of tax		18																										18
Comprehensive income		6,170
Adoption of new accounting standards		36,210	$ 3				3,347						1,097	1,537									(41)	18,505		14,088	$ 3	354
VE territory covered losses incurred		(17)											0	0									(17)
Recovery through conversion rate adjustment				$ 9	$ 6		(15)						$ 9	$ 6									15
Conversion of stock (in shares)											0					25	0	[1]			0	[1]
Conversion of stock								$ (1,724)																	$ 1,724
Vesting of restricted stock and performance-based shares (in shares)															3
Share-based compensation, net of forfeitures		275																						275
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		(140)																						(140)
Cash proceeds from issuance of common stock under employee equity plans (in shares)	[1]														1
Cash proceeds from issuance of class A common stock under employee equity plans		108																						108
Cash dividends declared and paid, at a quarterly amount per Class A share		(1,404)																								(1,404)
Repurchase of class A common stock (in shares)						(17)									(17)
Repurchase of class A common stock		(3,509)				$ (3,509)																		(183)		(3,326)
Ending balance (in shares) at Mar. 31, 2021									0	[1]			2	3	1,694				245	11
Ending balance at Mar. 31, 2021		37,696					3,347						$ 1,097	$ 1,537									(41)	18,505		15,513		372
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of new accounting standards		37,679					3,683																(34)	18,063		14,813		1,154
Beginning balance (in shares) at Dec. 31, 2020									0	[1]			2	3	1,696				245	11
Beginning balance at Dec. 31, 2020		37,679					3,683																(34)	18,063		14,813		1,154
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		3,026																								3,026
Other comprehensive income (loss), net of tax		(782)																										(782)
Comprehensive income		2,244
Adoption of new accounting standards		37,679					3,347						$ 1,097	$ 1,537									(41)	18,505		15,513		372
VE territory covered losses incurred		(7)																					(7)
Conversion of stock (in shares)											0					5	0	[1]			0	[1]
Conversion of stock								$ (336)																	$ 336
Vesting of restricted stock and performance-based shares (in shares)															0
Share-based compensation, net of forfeitures		153																						153
Restricted stock and performance-based shares settled in cash for taxes (in shares)															0
Restricted stock and performance-based shares settled in cash for taxes		(6)																						(6)
Cash proceeds from issuance of common stock under employee equity plans (in shares)	[1]														1
Cash proceeds from issuance of class A common stock under employee equity plans		47																						47
Cash dividends declared and paid, at a quarterly amount per Class A share		(701)																								(701)
Repurchase of class A common stock (in shares)						(8)									(8)
Repurchase of class A common stock		(1,713)				$ (1,713)																		(88)		(1,625)
Ending balance (in shares) at Mar. 31, 2021									0	[1]			2	3	1,694				245	11
Ending balance at Mar. 31, 2021		37,696					3,347						$ 1,097	$ 1,537									(41)	18,505		15,513		372
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of new accounting standards		$ 37,696					$ 3,347						$ 1,097	$ 1,537									$ (41)	$ 18,505		$ 15,513		$ 372

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