Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive (Loss) Income	Treasury Stock	Previously reported Retained Earnings	Previously reported Accumulated Other Comprehensive (Loss) Income
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustments from changes in accounting guidance, net of tax				$ 0	$ 0
Total stockholder's equity at beginning of period at Dec. 31, 2016		$ 683	$ 2,173	9,359	(173)	$ (73)	$ 9,359	$ (173)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			(6)			8
Dividends paid to common stockholders				(680)
Net income	$ 532			532
Other comprehensive (loss) income	205				205
Total stockholder's equity at end of period at Jun. 30, 2017	12,028	683	2,167	9,211	32	(65)
Total stockholder's equity at beginning of period at Mar. 31, 2017					(92)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	272
Other comprehensive (loss) income	124
Total stockholder's equity at end of period at Jun. 30, 2017	12,028	683	2,167	9,211	32	(65)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustments from changes in accounting guidance, net of tax				(50)	(16)
Total stockholder's equity at beginning of period at Dec. 31, 2017	12,244	683	2,175	9,364	16	(60)	$ 9,414	$ 32
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			4			2
Dividends paid to common stockholders				(709)
Net income	561			561
Other comprehensive (loss) income	(621)				(621)
Total stockholder's equity at end of period at Jun. 30, 2018	11,415	683	2,179	9,216	(605)	(58)
Total stockholder's equity at beginning of period at Mar. 31, 2018					(400)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	270
Other comprehensive (loss) income	(205)
Total stockholder's equity at end of period at Jun. 30, 2018	$ 11,415	$ 683	$ 2,179	$ 9,216	$ (605)	$ (58)