Consolidated Statements Of Stockholders' Equity - USD ($) $ in Millions	Common Stock [Member]	Retained Earnings [Member] Cumulative Effect, Period of Adoption, Adjustment [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member] Cumulative Effect, Period of Adoption, Adjustment [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
Balance as of beginning-of-period at Dec. 31, 2017	$ 5,693	$ (642)	$ 8,399	$ 642	$ 3,230
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
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	$ (203)	8,854		5,673	19,689
Stock compensation/issued for benefit plans	48
Net income (loss)			499			499
Retirement of common stock/cancellation of shares	(128)		(147)
Common stock dividends declared			(317)
Other comprehensive income (loss), net of tax					3,258	3,258
Balance as of end-of-period at Dec. 31, 2020	$ 5,082		$ 8,686		$ 8,931	$ 22,699