Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment [Member]	Common Stock [Member]	Preferred Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]	Retained Earnings [Member] Cumulative Effect, Period of Adoption, Adjustment [Member]
Balance at beginning of period at Dec. 31, 2017	$ 10,294	$ 40	$ 0	$ 0	$ 7,525	$ (768)	$ 3,537
Balance at beginning of period (Accounting Standards Update 2016-13 [Member]) at Dec. 31, 2017								$ 40
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,570						1,570
Other comprehensive loss	(298)					(298)
Stock based compensation	41				41
Issuance of preferred stock (Note 11)	492				492
Dividends paid (Note 11)	(434)						(434)
Dividends declared on preferred stock (Note 11)	(46)						(46)
Balance at end of period at Dec. 31, 2018	11,659		0	0	8,058	(1,066)	4,667
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,567						1,567
Other comprehensive loss	(53)					(53)
Stock based compensation	43				43
Dividends paid (Note 11)	(445)						(445)
Dividends declared on preferred stock (Note 11)	(45)						(45)
Balance at end of period at Dec. 31, 2019	12,726	$ (643)	0	0	8,101	(1,119)	5,744
Balance at end of period (Accounting Standards Update 2016-13 [Member]) at Dec. 31, 2019								$ (643)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	2,009						2,009
Other comprehensive loss	(190)					(190)
Stock based compensation	49				49
Issuance of preferred stock (Note 11)	492				492
Dividends paid (Note 11)	(845)						(845)
Balance at end of period at Dec. 31, 2020	$ 13,598		$ 0	$ 0	$ 8,642	$ (1,309)	$ 6,265