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			5			8
Dividends to common stockholders ($0.37, $0.35, $3.11 and $3.05 per share)				(833)
Net income	$ 727			727
Other comprehensive income	1,017				1,017
Purchase of treasury stock	(18)					(18)
Total stockholder's equity at end of period at Sep. 30, 2019	12,123	683	2,197	9,171	139	(67)
Total stockholder's equity at beginning of period at Jun. 30, 2019		683	2,190	9,159	120	(65)		9,159
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			7			0
Dividends to common stockholders ($0.37, $0.35, $3.11 and $3.05 per share)				(95)
Net income	107			107
Other comprehensive income	19				19
Purchase of treasury stock						(2)
Total stockholder's equity at end of period at Sep. 30, 2019	12,123	683	2,197	9,171	139	(67)
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			(1)			17
Dividends to common stockholders ($0.37, $0.35, $3.11 and $3.05 per share)				(850)
Net income	303			303
Other comprehensive income	360				360
Purchase of treasury stock	(18)					(18)
Total stockholder's equity at end of period at Sep. 30, 2020	12,021	683	2,202	8,796	411	(71)
Total stockholder's equity at beginning of period at Jun. 30, 2020		683	2,196	8,683	154	(71)		$ 8,683
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			6			0
Dividends to common stockholders ($0.37, $0.35, $3.11 and $3.05 per share)				(100)
Net income	213			213
Other comprehensive income	257				257
Total stockholder's equity at end of period at Sep. 30, 2020	$ 12,021	$ 683	$ 2,202	$ 8,796	$ 411	$ (71)