Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Retained Earnings Cumulative effect adjustments from changes in accounting guidance, net of tax	Retained Earnings Impact of adopting ASC 326	Accumulated Other Comprehensive Income	Treasury Stock
Total stockholder's equity at beginning of period at Dec. 31, 2019		$ 683	$ 2,203	$ 9,348	$ (5)	$ 9,343	$ 51	$ (70)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			(7)					17
Dividends to common stockholders ($0.38, $0.37, $1.51 and $2.74 per share)				(750)
Net income	$ 90			90
Other comprehensive income (loss)	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		8,634	(1,070)	(72)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			9					1
Dividends to common stockholders ($0.38, $0.37, $1.51 and $2.74 per share)				(102)
Net income	151			151
Other comprehensive income (loss)	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)
Total stockholder's equity at beginning of period at Dec. 31, 2020	12,707	683	2,211	9,081		9,081	803	(71)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			(10)					16
Dividends to common stockholders ($0.38, $0.37, $1.51 and $2.74 per share)				(413)
Net income	680			680
Other comprehensive income (loss)	(294)						(294)
Purchase of treasury stock	(18)							(18)
Total stockholder's equity at end of period at Jun. 30, 2021	12,668	683	2,201	9,348			509	(73)
Total stockholder's equity at beginning of period at Mar. 31, 2021		683	2,194	9,084		$ 9,084	187	(59)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			7					1
Dividends to common stockholders ($0.38, $0.37, $1.51 and $2.74 per share)				(104)
Net income	368			368
Other comprehensive income (loss)	322						322
Purchase of treasury stock								(15)
Total stockholder's equity at end of period at Jun. 30, 2021	$ 12,668	$ 683	$ 2,201	$ 9,348			$ 509	$ (73)