Condensed Consolidated Statements of Stockholders' Equity (Unaudited) (USD $) In Millions, unless otherwise specified	Total	Common stock [Member]	Additional paid-in capital [Member]	Retained earnings [Member]	Accumulated other comprehensive income (loss) [Member]	Treasury stock [Member]	Notes receivable for the issuance of common stock [Member]
Balance at Dec. 31, 2011		$ 683	$ 2,141	$ 8,308	$ 480	$ (102)	$ (22)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	637			637
Other comprehensive income (loss)	650				650
Dividends paid to common stockholders				(122)
Stock-based compensation			3			3
(Increase) decrease in notes receivable from the issuance of common stock							1
Balance at Sep. 30, 2012	12,660	683	2,144	8,823	1,130	(99)	(21)
Balance at Dec. 31, 2012	12,314	683	2,146	8,774	831	(99)	(21)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	716			716
Other comprehensive income (loss)	(718)				(718)
Dividends paid to common stockholders				(162)
Stock-based compensation			(4)			8
(Increase) decrease in notes receivable from the issuance of common stock							(1)
Balance at Sep. 30, 2013	$ 12,153	$ 683	$ 2,142	$ 9,328	$ 113	$ (91)	$ (22)