Consolidated Statements of Stockholders' Equity - 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 Balance, beginning of year, as adjusted	Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) Cumulative effect adjustments from changes in accounting guidance, net of tax	Accumulated Other Comprehensive Income (Loss) Balance, beginning of year, as adjusted	Treasury Stock
Total stockholder's equity at beginning of period at Dec. 31, 2017		$ 683	$ 2,175	$ 9,414	$ (50)	$ 9,364	$ 32	$ (16)	$ 16	$ (60)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			17							3
Dividends to common stockholders ($3.48, $3.40, and $3.30 per share)				(900)
Net income	$ 813			813
Other comprehensive income (loss)	(894)						(894)
Total stockholder's equity at end of period at Dec. 31, 2018	11,217	683	2,192	9,277		9,277	(878)		(878)	(57)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			11							10
Dividends to common stockholders ($3.48, $3.40, and $3.30 per share)				(929)
Net income	1,000			1,000
Other comprehensive income (loss)	929						929
Purchase of treasury stock										(23)
Total stockholder's equity at end of period at Dec. 31, 2019	12,215	683	2,203	9,348		$ 9,343	51		$ 51	(70)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			8							17
Dividends to common stockholders ($3.48, $3.40, and $3.30 per share)				(952)
Net income	690			690
Other comprehensive income (loss)	752						752
Purchase of treasury stock										(18)
Total stockholder's equity at end of period at Dec. 31, 2020	$ 12,707	$ 683	$ 2,211	$ 9,081	$ (5)		$ 803			$ (71)