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	58
Net income (loss)		846		$ 846
Retirement of common stock/cancellation of shares	(153)	(247)
Common stock dividends declared		(131)
Other comprehensive income (loss), net of tax			1,145	1,145
Balance as of end-of-period at Jun. 30, 2017	5,774	7,511	2,711	15,996
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	19
Net income (loss)		752		752
Retirement of common stock/cancellation of shares	(38)	(62)
Common stock dividends declared		(145)
Other comprehensive income (loss), net of tax			(2,671)	(2,671)
Balance as of end-of-period at Jun. 30, 2018	$ 5,674	$ 8,302	$ 1,201	$ 15,177