Net Income Per Common Share (Calculations For Basic And Diluted Earnings Per Share) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Numerator:
Net income-basic and diluted	$ 192	$ 111	$ 32	$ 86	$ 134	$ 19	$ (50)	$ 61	$ 421	$ 164	$ 375
Denominator:
Weighted-average common shares outstanding									162,504,000	162,667,000	162,778,000
Adjusted diluted weighted-average shares									163,661,000	163,259,000	163,274,000
Earnings per share:
Basic	$ 1.18	$ 0.69	$ 0.20	$ 0.53	$ 0.82	$ 0.12	$ (0.31)	$ 0.38	$ 2.59	$ 1.01	$ 2.30
Diluted	$ 1.17	$ 0.68	$ 0.20	$ 0.53	$ 0.82	$ 0.12	$ (0.31)	$ 0.38	$ 2.57	$ 1.01	$ 2.30
Number of anti-dilutive stock-based awards									5,938,000	7,758,000	9,538,000
Nonvested shares [Member]
Denominator:
Effect of stock-based awards									684,000,000	509,000,000	484,000,000
Stock Options [Member]
Denominator:
Effect of stock-based awards									473,000,000	83,000,000	12,000,000