Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Preferred shares	Common Shares	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Retained Earnings [Member]
Beginning Balance at Dec. 31, 2014	$ 20,673	$ 0	$ 205	$ 12,874	$ (1,919)	$ 9,513
Net income	5,163					5,163
Other comprehensive (loss) income	(615)				(615)
Repurchase of common shares	(4,509)		(12)	(714)		(3,783)
Other changes, primarily employee plans	310		1	347		(38)
Cash dividends declared preferred	(62)					(62)
Cash dividends declared common, per share	(1,128)					(1,128)
Ending Balance at Dec. 31, 2015	$ 20,673	0	194	$ 13,348	(2,534)	9,665
Preferred shares issued	841			841
Net income	$ 5,408					5,408
Other comprehensive (loss) income	(250)				(250)
Repurchase of common shares	(4,421)		(14)	$ (924)		(3,483)
Other changes, primarily employee plans	308		1	309	0	(2)
Cash dividends declared preferred	(80)					(80)
Cash dividends declared common, per share	(1,137)					(1,137)
Ending Balance at Dec. 31, 2016	$ 20,501	0	181	$ 12,733	(2,784)	10,371
Preferred shares issued	0			0
Net income	$ 2,736					2,736
Other comprehensive (loss) income	356				356
Repurchase of common shares	(4,314)		(10)	$ (742)		(3,562)
Other changes, primarily employee plans	212		1	219		(8)
Cash dividends declared preferred	(81)					(81)
Cash dividends declared common, per share	(1,183)					(1,183)
Ending Balance at Dec. 31, 2017	$ 18,227	$ 0	$ 172	$ 12,210	$ (2,428)	$ 8,273
Preferred shares issued	0