Accumulated Other Comprehensive Loss Reclassification Adjustments (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Interest expense		$ (11.5)	$ (8.0)
Investment income		4.9	7.9
Total reclassifications for the period		0.8	1.0
Interest Rate Hedges | Reclassification out of Accumulated Other Comprehensive Income [Member]
Interest expense		(0.1)	(0.1)
Net actuarial loss amortization | Reclassification out of Accumulated Other Comprehensive Income [Member]
Net periodic benefit cost	[1]	0.9	1.0
Net actuarial loss amortization, tax		(0.5)	(0.6)
Net prior service benefit amortization | Reclassification out of Accumulated Other Comprehensive Income [Member]
Net periodic benefit cost	[1]	0.0	0.1
Net prior service benefit amortization, amount recognized in other comprehensive income, tax		0.0	0.0
Pension and Other Post-retirement Benefits
Total reclassifications for the period		0.9	1.1
Pension and Other Post-retirement Benefits | Reclassification out of Accumulated Other Comprehensive Income [Member]
Net periodic benefit cost		0.9	1.1
Unrealized loss on securities | Reclassification out of Accumulated Other Comprehensive Income [Member]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax		$ 0.0	$ 0.0

[1] Pension and other post-retirement benefits AOCI components are included in the computation of net periodic benefit cost (refer to note 12).