Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Series B Preferred Stock [Member]	Series C Preferred Stock [Member]	Preferred shares	Common Shares	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Retained Earnings [Member]	Retained Earnings [Member] Series B Preferred Stock [Member]	Retained Earnings [Member] Series C Preferred Stock [Member]
Beginning Balance at Dec. 31, 2015	$ 20,673			$ 0	$ 194	$ 13,348	$ (2,534)	$ 9,665
Net income	5,375							5,375
Other comprehensive (loss) income	(250)						(250)	0
Repurchase of common shares	(4,421)				(14)	(924)		(3,483)
Other changes, primarily employee plans	308				1	309		(2)
Cash dividends declared preferred		$ (39)	$ (41)						$ (39)	$ (41)
Cash dividends declared common, per share	(1,137)							(1,137)
Ending Balance at Dec. 31, 2016	20,523			0	181	12,733	(2,784)	10,393
Cumulative Effect Of New Accounting Principle In Period Of Adoption	55							55
Net income	2,748							2,748
Other comprehensive (loss) income	356						356	0
Repurchase of common shares	(4,314)				(10)	(742)		(3,562)
Other changes, primarily employee plans	212				1	219	0	(8)
Cash dividends declared preferred		(39)	(42)						(39)	(42)
Cash dividends declared common, per share	(1,183)							(1,183)
Ending Balance at Dec. 31, 2017	18,261			0	172	12,210	(2,428)	8,307
Net income	6,921							6,921
Other comprehensive (loss) income	(169)						(169)	0
Repurchase of common shares	(1,570)				(3)	(216)		(1,351)
Other changes, primarily employee plans	200				1	224		(25)
Cash dividends declared preferred		$ (39)	$ (41)						$ (39)	$ (41)
Cash dividends declared common, per share	(1,273)							(1,273)
Ending Balance at Dec. 31, 2018	$ 22,290			$ 0	$ 170	$ 12,218	$ (2,597)	$ 12,499