Stockholder's Equity (Details) (USD $) In Millions, except Per Share data	1 Months Ended		3 Months Ended	9 Months Ended
	May 31, 2011	Feb. 28, 2011	Sep. 30, 2011	Sep. 30, 2011
Stockholders' Equity
Repurchase of common stock, authorized amount	$ 200	$ 150
Stock repurchased during the period, shares			2.9
Weighted average price per repurchased share			$ 16.57
Stock repurchased during the period, value			48.7
Remaining authorized amount available for stock repurchase				$ 73.2