Accumulated Other Comprehensive Income (Loss) Reclassification Adjustments (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Interest expense		$ (49.9)	$ (28.4)	$ (100.8)	$ (54.4)
Investment Income, Nonoperating		2.2	1.9	5.1	5.4
Total reclassifications for the period		4.8	2.6	4.8	4.8
Interest Rate Hedges | Reclassification out of Accumulated Other Comprehensive Income [Member]
Interest expense		0.5	0.8	1.0	1.2
Net actuarial loss amortization | Reclassification out of Accumulated Other Comprehensive Income [Member]
Net periodic benefit cost	[1]	4.3	1.8	3.8	3.6
Net actuarial loss amortization, tax		(0.4)	(0.6)	(0.7)	(0.2)
Pension and Other Post-retirement Benefits
Total reclassifications for the period		$ 4.3	$ 1.8	$ 3.8	$ 3.6

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