Accumulated Other Comprehensive Income (Loss) Reclassification Adjustments (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Interest expense		$ (26.0)	$ (30.8)
Investment Income, Nonoperating		3.5	6.4
Total reclassifications for the period		2.2	(4.2)
Interest Rate Hedges | Reclassification out of Accumulated Other Comprehensive Income [Member]
Interest expense		0.4	(0.3)
Net actuarial loss amortization | Reclassification out of Accumulated Other Comprehensive Income [Member]
Net periodic benefit cost	[1]	1.8	(3.9)
Net actuarial loss amortization, tax		(0.4)	1.5
Pension and Other Post-retirement Benefits
Total reclassifications for the period		$ 1.8	$ (3.9)

[1] Pension and other post-retirement benefits AOCI components are included in the computation of net periodic benefit cost (refer to note 16).