Condensed Consolidated Statement of Changes in Equity (unaudited) - USD ($) $ in Millions	Total	Series B Preferred Stock	Series C Preferred Stock	Cumulative Effect, Period of Adoption, Adjustment	Cumulative Effect, Period of Adoption, Adjusted Balance	Common stock and paid-in capital	Common stock and paid-in capital Cumulative Effect, Period of Adoption, Adjusted Balance	Preferred stock	Preferred stock Series B Preferred Stock	Preferred stock Series C Preferred Stock	Preferred stock Cumulative Effect, Period of Adoption, Adjusted Balance	Accumulated deficit	Accumulated deficit Series B Preferred Stock	Accumulated deficit Series C Preferred Stock	Accumulated deficit Cumulative Effect, Period of Adoption, Adjustment	Accumulated deficit Cumulative Effect, Period of Adoption, Adjusted Balance	Accumulated other comprehensive income (loss)	Accumulated other comprehensive income (loss) Cumulative Effect, Period of Adoption, Adjusted Balance	Treasury stock	Treasury stock Cumulative Effect, Period of Adoption, Adjusted Balance
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of Accounting Standards Update 2016-13	$ 14,416			$ (1,017)	$ 13,399	$ 21,438	$ 21,438	$ 0			$ 0	$ (4,057)			$ (1,017)	$ (5,074)	$ 123	$ 123	$ (3,088)	$ (3,088)
Beginning balance at Dec. 31, 2019	14,416			$ (1,017)	$ 13,399	21,438	$ 21,438	0			$ 0	(4,057)			$ (1,017)	$ (5,074)	123	$ 123	(3,088)	$ (3,088)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	398											398
Share-based compensation	79					79
Other comprehensive income (loss)	572																572
Common stock repurchases	(105)																		(105)
Common stock dividends	(217)											(217)
Ending balance at Sep. 30, 2020	14,126					21,517		0				(4,893)					695		(3,193)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of Accounting Standards Update 2016-13	13,826					21,499		0				(5,296)					815		(3,192)
Beginning balance at Jun. 30, 2020	13,826					21,499		0				(5,296)					815		(3,192)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	476											476
Share-based compensation	18					18
Other comprehensive income (loss)	(120)																(120)
Common stock repurchases	(1)																		(1)
Common stock dividends	(73)											(73)
Ending balance at Sep. 30, 2020	14,126					21,517		0				(4,893)					695		(3,193)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of Accounting Standards Update 2016-13	14,126					21,517		0				(4,893)					695		(3,193)
Adoption of Accounting Standards Update 2016-13	14,703					21,544		0				(4,278)					631		(3,194)
Beginning balance at Dec. 31, 2020	14,703					21,544		0				(4,278)					631		(3,194)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	2,408											2,408
Net proceeds from issuance of series preferred stock		$ 1,335	$ 989						$ 1,335	$ 989
Preferred stock dividends		(20)	(9)										$ (20)	$ (9)
Share-based compensation	100					100
Other comprehensive income (loss)	(580)																(580)
Common stock repurchases	(1,400)																		(1,400)
Common stock dividends	(237)											(237)
Ending balance at Sep. 30, 2021	17,289					21,644		2,324				(2,136)					51		(4,594)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of Accounting Standards Update 2016-13	17,530					21,631		2,324				(2,726)					216		(3,915)
Beginning balance at Jun. 30, 2021	17,530					21,631		2,324				(2,726)					216		(3,915)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	712											712
Preferred stock dividends		$ (20)	$ (9)										$ (20)	$ (9)
Share-based compensation	13					13
Other comprehensive income (loss)	(165)																(165)
Common stock repurchases	(679)																		(679)
Common stock dividends	(93)											(93)
Ending balance at Sep. 30, 2021	17,289					21,644		2,324				(2,136)					51		(4,594)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of Accounting Standards Update 2016-13	$ 17,289					$ 21,644		$ 2,324				$ (2,136)					$ 51		$ (4,594)