Income Taxes Schedule of Deferred Tax Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Assets:
Loss carryovers	$ 52.2	$ 52.6
Reserves not currently deductible for tax	94.5	91.2
Other	69.3	64.6
Gross deferred tax assets before valuation allowance	216.0	208.4
Valuation allowance	(0.9)	(2.7)
Net deferred tax assets	215.1	205.7
Liabilities:
Property	(1,194.7)	(1,044.6)
Investments	(68.2)	(66.3)
Other	(8.4)	(7.8)
Gross deferred tax liabilities	(1,271.3)	(1,118.7)
Net deferred tax liability	$ (1,056.2)	$ (913.0)