Stock-Based Compensation (Details 4) (Management Stock Purchase Plan, Restricted stock units (RSUs), USD $) In Millions, except Share data in Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
RSU activity and related information
Outstanding at beginning of period (in shares)	361	350	297
Granted (in shares)	99	159	150
Cancelled/Forfeitures (in shares)	(10)	(21)	(7)
Settled (in shares)	(58)	(127)	(90)
Outstanding at end of period (in shares)	392	361	350
Vested at end of period (in shares)	157	105	131
Weighted Average Purchase Price
Outstanding at beginning of period (in dollars per share)	$ 16.92	$ 18.13	$ 21.86
Granted (in dollars per share)	$ 25.15	$ 19.87	$ 13.25
Cancelled/Forfeitures (in dollars per share)	$ 20.92	$ 16.68	$ 18.08
Settled (in dollars per share)	$ 18.01	$ 23.95	$ 22.31
Outstanding at end of period (in dollars per share)	$ 18.74	$ 16.92	$ 18.13
Vested at end of period (in dollars per share)	$ 15.57	$ 15.21	$ 21.12
Weighted Average Intrinsic Value
Outstanding at end of period (in dollars per share)	$ 15.47
Vested at end of period (in dollars per share)	$ 18.64
Aggregate intrinsic value of outstanding awards	$ 6.1
Aggregate intrinsic value of awards vested	2.9
Aggregate intrinsic value of awards settled	$ 1.2	$ 0.7	$ 0.1
Class A
Weighted Average Intrinsic Value
Company's closing Common Stock price (in dollars per share)	$ 34.21