Calculations for Basic and Diluted Earnings Per Share (Detail) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Numerator:
Net income-basic and diluted	$ 166	$ 377	$ 432
Denominator:
Weighted-average common shares outstanding	162,667,354	162,777,695	162,595,041
Adjusted diluted weighted-average shares	163,259,222	163,274,491	162,866,863
Earnings per share:
Basic	$ 1.02	$ 2.32	$ 2.66
Diluted	$ 1.02	$ 2.31	$ 2.65
Number of anti-dilutive stock-based awards	7,757,969	9,538,350	9,875,411
Nonvested shares
Denominator:
Effect of stock-based awards	509,177	484,829	271,822
Stock Options
Denominator:
Effect of stock-based awards	82,691	11,967