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)	416			416
Other comprehensive income (loss)	387				387
Dividends paid to common stockholders				(81)
Stock-based compensation						3
(Increase) decrease in notes receivable from the issuance of common stock							1
Balance at Jun. 30, 2012	12,214	683	2,141	8,643	867	(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)	444			444
Other comprehensive income (loss)	(705)				(705)
Dividends paid to common stockholders				(108)
Stock-based compensation			(6)			8
(Increase) decrease in notes receivable from the issuance of common stock							(3)
Balance at Jun. 30, 2013	$ 11,944	$ 683	$ 2,140	$ 9,110	$ 126	$ (91)	$ (24)