Income Taxes (Deferred Tax Assets and Liabilities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
DEFERRED TAX ASSETS:
Accrued liabilities	$ 87.8	$ 92.7
Accrued compensation and benefits	67.1	70.5
Net operating and capital loss carryforwards	22.2	22.9
Unrealized losses on investments	16.7	0
Insurance loss reserves and unearned premiums	12.7	15.4
Deferred gain in revenues	6.6	12.4
Other	8.8	2.4
Deferred tax assets before valuation alllowance	221.9	216.3
Valuation allowance	(23.3)	(19.7)
Net deferred tax assets	198.6	196.6
DEFERRED TAX LIABILITIES:
Depreciable and amortizable property	77.1	63.6
Prepaid expenses	14.9	17.7
Deferred revenue	13.2	25.8
Unrealized gains on investments	0	22.9
Other	4.0	1.9
Deferred tax liabilities	$ 109.2	$ 131.9