Investments - Unrealized Gains and Gross Unrealized Losses in Investment in Equity Securities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Equity Securities at Cost	$ 530.0	$ 462.7
Gross Unrealized Gains	74.7	62.5
Gross Unrealized Losses	(6.2)	(3.3)
Equity Securities at Fair Value	598.5	521.9
Preferred Stocks Finance, Insurance and Real Estate [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity Securities at Cost	85.4	75.4
Gross Unrealized Gains	2.9	3.9
Gross Unrealized Losses	(2.5)	(0.1)
Equity Securities at Fair Value	85.8	79.2
Preferred Stocks Other Industries [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity Securities at Cost	20.1	18.4
Gross Unrealized Gains	4.4	3.8
Gross Unrealized Losses	(0.1)	(0.9)
Equity Securities at Fair Value	24.4	21.3
Common Stocks Manufacturing [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity Securities at Cost	83.4	67.0
Gross Unrealized Gains	21.3	20.9
Gross Unrealized Losses	(0.1)	(0.4)
Equity Securities at Fair Value	104.6	87.5
Common Stock Other Industries [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity Securities at Cost	68.8	59.1
Gross Unrealized Gains	17.0	8.1
Gross Unrealized Losses	(0.9)	(0.5)
Equity Securities at Fair Value	84.9	66.7
Exchange Traded Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity Securities at Cost	122.0	119.6
Gross Unrealized Gains	3.9	6.3
Gross Unrealized Losses	(1.0)	0
Equity Securities at Fair Value	124.9	125.9
Limited Liability Companies and Limited Partnerships [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity Securities at Cost	150.3	123.2
Gross Unrealized Gains	25.2	19.5
Gross Unrealized Losses	(1.6)	(1.4)
Equity Securities at Fair Value	$ 173.9	$ 141.3