Stock-Based Compensation - RSU activity (Details) - Management Stock Purchase Plan - Restricted stock units (RSUs) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
RSU activity and related information
Outstanding at beginning of period (in shares)	101	80	132
Granted (in shares)	89	60	31
Cancelled/Forfeitures (in shares)	(28)	(9)	(32)
Settled (in shares)	(14)	(30)	(51)
Outstanding at end of period (in shares)	148	101	80
Vested at end of period (in shares)	28	25	31
Weighted Average Purchase Price
Outstanding at beginning of period (in dollars per share)	$ 36.14	$ 32.08	$ 27.46
Granted (in dollars per share)	35.41	37.13	40.27
Cancelled/Forfeitures (in dollars per share)	32.25	36.92	31.58
Settled (in dollars per share)	36.91	27.10	25.41
Outstanding at end of period (in dollars per share)	36.37	36.14	32.08
Vested at end of period (in dollars per share)	37.78	$ 33.35	$ 27.96
Weighted Average Intrinsic Value
Outstanding at end of period (in dollars per share)	13.53
Vested at end of period (in dollars per share)	$ 16.32
Aggregate intrinsic value of outstanding awards	$ 4.3
Aggregate intrinsic vlaue of awards vested	0.8
Total intrinsic value of awards settled	$ 1.5	$ 0.8	$ 1.7