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)	250			250
Other comprehensive income (loss)					284
Dividends paid to common stockholders				(41)
Stock-based compensation			(1)			2
(Increase) decrease in notes receivable from the issuance of common stock							(1)
Balance at Mar. 31, 2012	11,981	683	2,140	8,517	764	(100)	(23)
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)	250			250
Other comprehensive income (loss)					(104)
Dividends paid to common stockholders				(55)
Stock-based compensation			(8)			7
(Increase) decrease in notes receivable from the issuance of common stock							1
Balance at Mar. 31, 2013	$ 12,405	$ 683	$ 2,138	$ 8,969	$ 727	$ (92)	$ (20)