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, 2016	$ 5,869	$ 7,043	$ 1,566
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
Balance as of beginning-of-year 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	33
Net income (loss)		1,242		1,242
Retirement of common stock/cancellation of shares	(107)	(168)
Common stock dividends declared		(216)
Other comprehensive income (loss), net of tax			(3,036)	(3,036)
Balance as of end-of-period at Sep. 30, 2018	$ 5,619	$ 8,615	$ 836	$ 15,070