Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Series C Preferred Stock [Member]	Preferred shares	Common shares	Additional Paid In Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Retained Earnings [Member] Series C Preferred Stock [Member]
Beginning Balance at Dec. 31, 2017	$ 18,261		$ 0	$ 172	$ 12,210	$ (2,428)	$ 8,307
Net income	1,634		0	0	0	0	1,634
Other comprehensive income (loss)	47		0	0	0	47	0
Repurchase of common shares	0		0	0	0	0	0
Other changes, primarily employee plans	(7)		0	0	15	0	(22)
Cash dividends declared preferred		$ (21)	0	0	0	0		$ (21)
Cash dividends declared common	(301)		0	0	0	0	(301)
Ending Balance at Mar. 31, 2018	19,613		0	172	12,225	(2,381)	9,597
Beginning Balance at Dec. 31, 2018	22,290		0	170	12,218	(2,597)	12,499
Net income	1,550		0	0	0	0	1,550
Other comprehensive income (loss)	(2)		0	0	0	(2)	0
Repurchase of common shares	(1,245)		0	(3)	(267)	0	(975)
Other changes, primarily employee plans	(27)		0	1	12	0	(40)
Cash dividends declared preferred		$ (21)	0	0	0	0		$ (21)
Cash dividends declared common	(327)		0	0	0	0	(327)
Ending Balance at Mar. 31, 2019	$ 22,218		$ 0	$ 168	$ 11,963	$ (2,599)	$ 12,686