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	28
Net income (loss)			454		$ 454
Retirement of common stock/cancellation of shares	(228)		(222)
Common stock dividends declared			(224)
Other comprehensive income (loss), net of tax				5,841	5,841
Balance as of end-of-period at Sep. 30, 2019	5,192		8,559	6,248	19,999
Balance as of beginning-of-period at Jun. 30, 2019	5,241		8,878	4,336
Stock compensation/issued for benefit plans	17
Net income (loss)			(161)		(161)
Retirement of common stock/cancellation of shares	(66)		(84)
Common stock dividends declared			(74)
Other comprehensive income (loss), net of tax				1,912	1,912
Balance as of end-of-period at Sep. 30, 2019	5,192		8,559	6,248	19,999
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	31
Net income (loss)			356		356
Retirement of common stock/cancellation of shares	(100)		(125)
Common stock dividends declared			(235)
Other comprehensive income (loss), net of tax				2,136	2,136
Balance as of end-of-period at Sep. 30, 2020	5,093		8,647	7,809	21,549
Balance as of beginning-of-period at Jun. 30, 2020	5,081		8,327	7,323
Stock compensation/issued for benefit plans	12
Net income (loss)			398		398
Common stock dividends declared			(78)
Other comprehensive income (loss), net of tax				486	486
Balance as of end-of-period at Sep. 30, 2020	$ 5,093		$ 8,647	$ 7,809	$ 21,549