Earnings Per Common Share - Numerators and Denominators Used in Computations of Basic and Diluted Earnings Per Common Share (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Numerator (basic and diluted):
Income from continuing operations	$ 105	$ 26	$ 243	$ 17
Allocation to unvested restricted stock awards	(2)	(1)	(5)	(2)
Income from continuing operations attributable to common shareholders	103	25	238	15
Loss from discontinued operations, net	(2)	(11)	(16)	(44)
Allocation to unvested restricted stock awards				1
Loss from discontinued operations attributable to common shareholders	(2)	(11)	(16)	(43)
Net income (loss) available to common shareholders	$ 101	$ 14	$ 222	$ (28)
Denominator:
Basic common shares (based upon weighted average)	349	349	349	349
Contingent common shares
Stock option dilution	3	1	3	1
Diluted common shares	352	350	352	350