Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Series B [Member]	Series C [Member]	Preferred Shares [Member]	Common Shares [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]	Retained Earnings [Member] Series B [Member]	Retained Earnings [Member] Series C [Member]
Beginning Balance at Dec. 31, 2016	$ 20,523			$ 0	$ 181	$ 12,733	$ (2,784)	$ 10,393
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		(8)
Cash dividends declared preferred		$ (39)	$ (42)						$ (39)	$ (42)
Cash dividends declared common	(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	(1,273)							(1,273)
Ending Balance at Dec. 31, 2018	22,290			0	170	12,218	(2,597)	12,499
Net income	6,759							6,759
Other comprehensive (loss) income	(140)						(140)	0
Repurchase of common shares	(4,585)				(8)	(671)		(3,906)
Other changes, primarily employee plans	186				1	227		(42)
Cash dividends declared preferred		$ (39)	$ (42)						$ (39)	$ (42)
Cash dividends declared common	(1,358)							(1,358)
Ending Balance at Dec. 31, 2019	$ 23,071			$ 0	$ 163	$ 11,774	$ (2,737)	$ 13,871