Consolidated Statements Of Stockholders' Equity - USD ($) $ in Millions	Common Stock	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	3
Net income (loss)		211		$ 211
Retirement of common stock/cancellation of shares	(142)	(58)
Common stock dividends declared		(59)
Other comprehensive income (loss), net of tax			1,086	1,086
Balance as of end-of-period at Mar. 31, 2016	6,159	6,568	1,931	14,658
Balance as of beginning-of-year at Dec. 31, 2016	5,869	7,043	1,566	14,478
Stock compensation/issued for benefit plans	44
Net income (loss)		435		435
Retirement of common stock/cancellation of shares	(74)	(126)
Common stock dividends declared		(65)
Other comprehensive income (loss), net of tax			281	281
Balance as of end-of-period at Mar. 31, 2017	$ 5,839	$ 7,287	$ 1,847	$ 14,973