Stock-based Compensation (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award
Share-based compensation arrangement by share-based payment award, restricted stock units, award measurement period for market-based awards			3 years
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation expense for nonvested stock units	$ 12.7	$ 11.8	$ 31.0	$ 31.6
Performance-based Restricted Stock Units | Minimum
Share-based Compensation Arrangement by Share-based Payment Award
Share-based compensation arrangement by share-based payment award, restricted stock units, expected payout (in shares)			0
Performance-based Restricted Stock Units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award
Share-based compensation arrangement by share-based payment award, restricted stock units, expected payout (in shares)			774,000