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	33
Net income (loss)		1,242		$ 1,242
Retirement of common stock/cancellation of shares	(107)	(168)
Common stock dividends declared		(216)
Other comprehensive income (loss), net of tax			(3,036)	(3,036)
Balance as of end-of-period at Sep. 30, 2018	5,619	8,615	836	15,070
Balance as of beginning-of-period at Jun. 30, 2018	5,674	8,302	1,201
Stock compensation/issued for benefit plans	14
Net income (loss)		490		490
Retirement of common stock/cancellation of shares	(69)	(106)
Common stock dividends declared		(71)
Other comprehensive income (loss), net of tax			(365)	(365)
Balance as of end-of-period at Sep. 30, 2018	5,619	8,615	836	15,070
Balance as of beginning-of-period at Dec. 31, 2018	5,392	8,551	407	14,350
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