Consolidated Statements Of Stockholders' Equity - USD ($) $ in Millions	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
Balance as of beginning-of-year at Dec. 31, 2015	$ 6,298	$ 6,474	$ 845
Stock compensation/issued for benefit plans	23
Net income (loss)		1,002		$ 1,002
Retirement of common stock/cancellation of shares	(415)	(260)
Common stock dividends declared		(176)
Other comprehensive income (loss), net of tax			2,532	2,532
Balance as of end-of-period at Sep. 30, 2016	5,906	7,040	3,377	16,323
Balance as of beginning-of-year at Dec. 31, 2016	5,869	7,043	1,566	14,478
Stock compensation/issued for benefit plans	75
Net income (loss)		1,264		1,264
Retirement of common stock/cancellation of shares	(227)	(373)
Common stock dividends declared		(196)
Other comprehensive income (loss), net of tax			1,293	1,293
Balance as of end-of-period at Sep. 30, 2017	$ 5,717	$ 7,738	$ 2,859	$ 16,314