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			(1)					17
Dividends to common stockholders ($0.38, $0.37, $1.89 and $3.11 per share)				(850)
Net income	$ 303			303
Other comprehensive (loss) 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		8,683	154	(71)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			6					0
Dividends to common stockholders ($0.38, $0.37, $1.89 and $3.11 per share)				(100)
Net income	213			213
Other comprehensive (loss) income	257						257
Purchase of treasury stock								0
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 Dec. 31, 2020	12,707	683	2,211	9,081		9,081	803	(71)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			(3)					16
Dividends to common stockholders ($0.38, $0.37, $1.89 and $3.11 per share)				(517)
Net income	936			936
Other comprehensive (loss) income	(457)						(457)
Purchase of treasury stock	(18)							(18)
Total stockholder's equity at end of period at Sep. 30, 2021	12,664	683	2,208	9,500			346	(73)
Total stockholder's equity at beginning of period at Jun. 30, 2021		683	2,201	9,348		$ 9,348	509	(73)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			7					0
Dividends to common stockholders ($0.38, $0.37, $1.89 and $3.11 per share)				(104)
Net income	256			256
Other comprehensive (loss) income	(163)						(163)
Purchase of treasury stock								0
Total stockholder's equity at end of period at Sep. 30, 2021	$ 12,664	$ 683	$ 2,208	$ 9,500			$ 346	$ (73)