Accumulated Other Comprehensive Income - Reclasses Out Of AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	$ 354.8	$ 330.6
Other comprehensive income	34.3	25.2
Ending balance	421.2	350.2
Benefit Plan Adjustments
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	(559.6)
Other comprehensive income (loss) before reclassifications	(1.3)
Amounts reclassified from accumulated other comprehensive loss	8.1
Other comprehensive income	6.8	7.3
Ending balance	(552.8)
Foreign Currency Translation Adjustments
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	(349.1)
Other comprehensive income (loss) before reclassifications	26.3
Amounts reclassified from accumulated other comprehensive loss	0.0
Other comprehensive income	26.3	17.1
Ending balance	(322.8)
Unrealized Gains (Losses) on Available-for-Sale Securities
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	1.0
Other comprehensive income (loss) before reclassifications	0.1
Amounts reclassified from accumulated other comprehensive loss	0.0
Other comprehensive income	0.1	0.2
Ending balance	1.1
Gains (Losses) on Cash Flow Hedges
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	0.7
Other comprehensive income (loss) before reclassifications	(0.2)
Amounts reclassified from accumulated other comprehensive loss	0.2
Other comprehensive income	0.0	(0.2)
Ending balance	0.7
Accumulated Other Comprehensive Loss
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Beginning balance	(907.0)	(891.9)
Other comprehensive income (loss) before reclassifications	24.9
Amounts reclassified from accumulated other comprehensive loss	8.3
Other comprehensive income	33.2	24.4
Ending balance	$ (873.8)	$ (867.5)