Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	AOCI Attributable to Parent	Treasury Stock
Balance, beginning of year at Dec. 31, 2015		$ 683	$ 2,153	$ 9,313	$ (315)	$ (78)
Stock-based compensation			2			5
Dividends paid to common stockholders				(677)
Net income	$ 275			275
Other comprehensive income	525				525
Balance, end of period at Jun. 30, 2016	11,886	683	2,155	8,911	210	(73)
Balance, beginning of year at Mar. 31, 2016					(56)
Net income	209
Other comprehensive income	266
Balance, end of period at Jun. 30, 2016	11,886	683	2,155	8,911	210	(73)
Balance, beginning of year at Dec. 31, 2016	11,969	683	2,173	9,359	(173)	(73)
Stock-based compensation			(6)			8
Dividends paid to common stockholders				(680)
Net income	532			532
Other comprehensive income	205				205
Balance, end of period at Jun. 30, 2017	12,028	683	2,167	9,211	32	(65)
Balance, beginning of year at Mar. 31, 2017					(92)
Net income	272
Other comprehensive income	124
Balance, end of period at Jun. 30, 2017	$ 12,028	$ 683	$ 2,167	$ 9,211	$ 32	$ (65)