Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income	Treasury Stock	Cumulative effect adjustments from changes in accounting guidance, net of tax Retained Earnings	Balance, beginning of period, as adjusted Retained Earnings
Total stockholder's equity at beginning of period at Dec. 31, 2018		$ 683	$ 2,192	$ 9,277	$ (878)	$ (57)		$ 9,277
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			(2)			8
Dividends to common stockholders ($0.37, $0.35, $2.74 and $2.70 per share)				(738)
Net income	$ 620			620
Other comprehensive income	998				998
Purchase of treasury stock	16					(16)
Total stockholder's equity at end of period at Jun. 30, 2019	12,087	683	2,190	9,159	120	(65)
Total stockholder's equity at beginning of period at Mar. 31, 2019		683	2,184	8,976	(324)	(64)		8,976
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			6			1
Dividends to common stockholders ($0.37, $0.35, $2.74 and $2.70 per share)				(95)
Net income	278			278
Other comprehensive income	444				444
Purchase of treasury stock						(2)
Total stockholder's equity at end of period at Jun. 30, 2019	12,087	683	2,190	9,159	120	(65)
Total stockholder's equity at beginning of period at Dec. 31, 2019	12,215	683	2,203	9,348	51	(70)	$ (5)	9,343
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			(7)			17
Dividends to common stockholders ($0.37, $0.35, $2.74 and $2.70 per share)				(750)
Net income	90			90
Other comprehensive income	103				103
Purchase of treasury stock	18					(18)
Total stockholder's equity at end of period at Jun. 30, 2020	11,645	683	2,196	8,683	154	(71)
Total stockholder's equity at beginning of period at Mar. 31, 2020		683	2,187	8,634	(1,070)	(72)		$ 8,634
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			9			1
Dividends to common stockholders ($0.37, $0.35, $2.74 and $2.70 per share)				(102)
Net income	151			151
Other comprehensive income	1,224				1,224
Total stockholder's equity at end of period at Jun. 30, 2020	$ 11,645	$ 683	$ 2,196	$ 8,683	$ 154	$ (71)