Income Taxes (Deferred Tax Assets and Liabilities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
DEFERRED TAX ASSETS:
Accrued liabilities	$ 92.7	$ 71.2
Accrued compensation and benefits	70.5	79.6
Net operating and capital loss carryforwards	22.9	75.2
Insurance loss reserves and unearned premiums	15.4	17.4
Deferred gain in revenues	12.4	12.4
Other	2.4	0.8
Deferred tax assets before valuation alllowance	216.3	256.6
Valuation allowance	(19.7)	(63.7)
Net deferred tax assets	196.6	192.9
DEFERRED TAX LIABILITIES:
Depreciable and amortizable property	63.6	51.0
Prepaid expenses	17.7	23.4
Unrealized gains on investments	22.9	11.6
Deferred revenue	25.8	8.3
Other	1.9	2.3
Deferred tax liabilities	$ 131.9	$ 96.6