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, 2014	Dec. 31, 2013	Dec. 31, 2012
Management Stock Purchase Plan | Restricted stock units (RSUs)
RSU activity and related information
Outstanding at beginning of period (in shares)	132	196	392
Granted (in shares)	31	45	64
Cancelled/Forfeitures (in shares)	(32)	(14)	(110)
Settled (in shares)	(51)	(95)	(150)
Outstanding at end of period (in shares)	80	132	196
Vested at end of period (in shares)	31	42	81
Weighted Average Purchase Price
Outstanding at beginning of period (in dollars per share)	$ 27.46	$ 22.88	$ 18.74
Granted (in dollars per share)	$ 40.27	$ 31.63
Cancelled/Forfeitures (in dollars per share)	$ 31.58	$ 28.35
Settled (in dollars per share)	$ 25.41	$ 19.19
Outstanding at end of period (in dollars per share)	$ 32.08	$ 27.46	$ 22.88
Vested at end of period (in dollars per share)	$ 27.96	$ 25.30	$ 20.36
Weighted Average Intrinsic Value
Outstanding at end of period (in dollars per share)	$ 31.36
Vested at end of period (in dollars per share)	$ 35.48
Aggregate intrinsic value of outstanding awards	$ 2.5
Aggregate intrinsic value of awards vested	1.1
Aggregate intrinsic value of awards settled	$ 1.7	$ 2.8	$ 3.8