Consolidated Statements of Changes in Stockholder's Equity - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests
Beginning balance at Dec. 31, 2013	$ 14,885	$ 144	$ 7,418	$ 7,681	$ (645)	$ 287
Net Income Including Noncontrolling Interests	763			782		(19)
Other comprehensive income (loss), net of tax	(84)				(84)
Compensation—restricted stock units	10		10
Capital contribution	231		231
Other	7		1	10		(4)
Net change	927		242	792	(84)	(23)
Ending balance at Dec. 31, 2014	15,812	144	7,660	8,473	(729)	264
Net Income Including Noncontrolling Interests	599			644		(45)
Other comprehensive income (loss), net of tax	(21)				(21)
Compensation—restricted stock units	9		9
Capital contribution	200		200
Other	(6)		(1)	(1)		(4)
Net change	781		208	643	(21)	(49)
Ending balance at Dec. 31, 2015	16,593	144	7,868	9,116	(750)	215
Net Income Including Noncontrolling Interests	922			990		(68)
Other comprehensive income (loss), net of tax	(146)				(146)
Compensation—restricted stock units	10		13	(3)
Other	7		3	(2)		6
Net change	793		16	985	(146)	(62)
Ending balance at Dec. 31, 2016	$ 17,386	$ 144	$ 7,884	$ 10,101	$ (896)	$ 153