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, 2017	$ 5,693	$ 8,399	$ 3,230
Cumulative effect from adoption of new accounting standards at Dec. 31, 2017		(642)	642
Stock compensation/issued for benefit plans	7
Net income (loss)		367		$ 367
Common stock dividends declared		(72)
Other comprehensive income (loss), net of tax			(1,639)	(1,639)
Balance as of end-of-period at Mar. 31, 2018	5,700	8,052	2,233	15,985
Balance as of beginning-of-year at Dec. 31, 2018	5,392	8,551	407	14,350
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