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-period at Dec. 31, 2016	$ 5,869	$ 7,043	$ 1,566
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
Cumulative effect from adoption of new accounting standards at Dec. 31, 2018				(6)
Stock compensation/issued for benefit plans	42
Net income (loss)		886		886
Retirement of common stock/cancellation of shares	(272)	(278)
Common stock dividends declared		(305)
Other comprehensive income (loss), net of tax			5,266	5,266
Balance as of end-of-period at Dec. 31, 2019	$ 5,162	$ 8,854	$ 5,673	$ 19,689