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, 2014	$ 6,622	$ 6,022	$ 3,096
Stock compensation/issued for benefit plans	88
Net income (loss)		1,154		$ 1,154
Retirement of common stock/cancellation of shares	(412)	(488)
Common stock dividends declared		(214)
Other comprehensive income (loss), net of tax			(2,251)	(2,251)
Balance as of end-of-year at Dec. 31, 2015	6,298	6,474	845	13,617
Stock compensation/issued for benefit plans	70
Net income (loss)		1,192		1,192
Retirement of common stock/cancellation of shares	(499)	(380)
Common stock dividends declared		(243)
Other comprehensive income (loss), net of tax			721	721
Balance as of end-of-year at Dec. 31, 2016	5,869	7,043	1,566	14,478
Stock compensation/issued for benefit plans	94
Net income (loss)		2,079		2,079
Retirement of common stock/cancellation of shares	(270)	(455)
Common stock dividends declared		(268)
Other comprehensive income (loss), net of tax			1,664	1,664
Balance as of end-of-year at Dec. 31, 2017	$ 5,693	$ 8,399	$ 3,230	$ 17,322