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, 2018	$ 5,392	$ 8,551	$ 407
Stock compensation/issued for benefit plans	(5)
Net income (loss)		252		$ 252
Retirement of common stock/cancellation of shares	(102)	(48)
Common stock dividends declared		(76)
Other comprehensive income (loss), net of tax			2,046	2,046
Balance as of end-of-period at Mar. 31, 2019	5,285	8,679	2,453	16,417
Balance as of beginning-of-year at Dec. 31, 2019	5,162	8,854	5,673	19,689
Cumulative effect from adoption of new accounting standards at Dec. 31, 2019		(203)
Stock compensation/issued for benefit plans	9
Net income (loss)		52		52
Retirement of common stock/cancellation of shares	(100)	(125)
Common stock dividends declared		(78)
Other comprehensive income (loss), net of tax			(2,669)	(2,669)
Balance as of end-of-period at Mar. 31, 2020	$ 5,071	$ 8,500	$ 3,004	$ 16,575