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, 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	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
Balance as of beginning-of-period at Mar. 31, 2018	5,700	8,052	2,233
Stock compensation/issued for benefit plans	12
Net income (loss)		385		385
Retirement of common stock/cancellation of shares	(38)	(62)
Common stock dividends declared		(73)
Other comprehensive income (loss), net of tax			(1,032)	(1,032)
Balance as of end-of-period at Jun. 30, 2018	5,674	8,302	1,201	15,177
Balance as of beginning-of-period at Dec. 31, 2018	5,392	8,551	407	14,350
Stock compensation/issued for benefit plans	11
Net income (loss)		616		616
Retirement of common stock/cancellation of shares	(162)	(138)
Common stock dividends declared		(151)
Other comprehensive income (loss), net of tax			3,929	3,929
Balance as of end-of-period at Jun. 30, 2019	5,241	8,878	4,336	18,455
Balance as of beginning-of-period at Mar. 31, 2019	5,285	8,679	2,453
Stock compensation/issued for benefit plans	16
Net income (loss)		363		363
Retirement of common stock/cancellation of shares	(60)	(90)
Common stock dividends declared		(74)
Other comprehensive income (loss), net of tax			1,883	1,883
Balance as of end-of-period at Jun. 30, 2019	$ 5,241	$ 8,878	$ 4,336	$ 18,455