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, 2015	$ 6,298	$ 6,474	$ 845
Stock compensation/issued for benefit plans	11
Net income (loss)		536		$ 536
Retirement of common stock/cancellation of shares	(303)	(172)
Common stock dividends declared		(119)
Other comprehensive income (loss), net of tax			2,350	2,350
Balance as of end-of-period at Jun. 30, 2016	6,006	6,719	3,195	15,920
Balance as of beginning-of-year at Dec. 31, 2016	5,869	7,043	1,566	14,478
Stock compensation/issued for benefit plans	58
Net income (loss)		846		846
Retirement of common stock/cancellation of shares	(153)	(247)
Common stock dividends declared		(131)
Other comprehensive income (loss), net of tax			1,145	1,145
Balance as of end-of-period at Jun. 30, 2017	$ 5,774	$ 7,511	$ 2,711	$ 15,996