Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Notes Receivable for the Issuance of Common Stock
Total stockholder's equity at beginning of period at Dec. 31, 2014		$ 683	$ 2,151	$ 9,645	$ 400	$ (84)	$ (1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			2			6
Dividends paid to common stockholders				(811)
Net income	$ 479			479
Other comprehensive income (loss)	(715)				(715)
Decrease in notes receivable for common stock							1
Total stockholder's equity at end of period at Dec. 31, 2015	11,756	683	2,153	9,313	(315)	(78)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			20			5
Dividends paid to common stockholders				(813)
Net income	859			859
Other comprehensive income (loss)	142				142
Decrease in notes receivable for common stock							0
Total stockholder's equity at end of period at Dec. 31, 2016	11,969	683	2,173	9,359	(173)	(73)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation			2			13
Dividends paid to common stockholders				(844)
Net income	899			899
Other comprehensive income (loss)	205				205
Decrease in notes receivable for common stock							$ 0
Total stockholder's equity at end of period at Dec. 31, 2017	$ 12,244	$ 683	$ 2,175	$ 9,414	$ 32	$ (60)