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]	Total
Balance as of beginning-of-period at Dec. 31, 2018	$ 5,392		$ 8,551	$ 407
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
Balance as of beginning-of-period at Dec. 31, 2019	5,162	$ (203)	8,854	5,673	19,689
Stock compensation/issued for benefit plans	19
Net income (loss)			(42)		(42)
Retirement of common stock/cancellation of shares	(100)		(125)
Common stock dividends declared			(157)
Other comprehensive income (loss), net of tax				1,650	1,650
Balance as of end-of-period at Jun. 30, 2020	5,081		8,327	7,323	20,731
Balance as of beginning-of-period at Mar. 31, 2020	5,071		8,500	3,004
Stock compensation/issued for benefit plans	10
Net income (loss)			(94)		(94)
Common stock dividends declared			(79)
Other comprehensive income (loss), net of tax				4,319	4,319
Balance as of end-of-period at Jun. 30, 2020	$ 5,081		$ 8,327	$ 7,323	$ 20,731