Capital Stock (Narrative) (Detail) (USD $) In Millions, except Share data, unless otherwise specified	9 Months Ended			1 Months Ended		9 Months Ended				1 Months Ended
	Sep. 30, 2012	Feb. 29, 2012	Dec. 31, 2011	Sep. 30, 2012 Series B Preferred Stock [Member]	May 31, 2012 Series B Preferred Stock [Member]	Sep. 30, 2012 Series B Preferred Stock [Member] Convertible Preferred Stock [Member]	Sep. 30, 2012 Common Stock [Member]	Sep. 30, 2012 Barclays [Member]	Sep. 30, 2012 Barclays [Member] Common Stock [Member]	May 29, 2012 Barclays Bank PLC ("Barclays") [Member]	May 31, 2012 Barclays Bank PLC ("Barclays") [Member]
Schedule of Capitalization, Equity [Line Items]
Share repurchase program authorized amount		5,000,000
Common shares repurchased	1,858,100							35,210,021	31,516
Common shares repurchased, value	$ 334
Shares authorized to be repurchased	3,593,900
Common stock issued upon the conversion of Series B Convertible										26,211,335	26,211,335
Common stock, par value	$ 0.01		$ 0.01							$ 160.00	$ 160.00
Repurchased shares from Barclays								6,377,552
Repurchased shares price								$ 156.80
Preferred shares						6,346,036
Common stock				593,786	2,000,000		31,516
Underwriters' option to purchase additional shares							2,621,134
Purchase additional shares in the secondary offering								35,210,021