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	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-period 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-period at Dec. 31, 2017	5,693	8,399	3,230	17,322
Cumulative effect from adoption of new accounting standards at Dec. 31, 2017		(642)	642
Stock compensation/issued for benefit plans	45
Net income (loss)		1,641		1,641
Retirement of common stock/cancellation of shares	(346)	(554)
Common stock dividends declared		(293)
Other comprehensive income (loss), net of tax			(3,465)	(3,465)
Balance as of end-of-period at Dec. 31, 2018	$ 5,392	$ 8,551	$ 407	$ 14,350