Investments (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]
Annual funding obligation	$ 36.4
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis	28.9	15.0
Available-for-sale securities, fair value	32.7	17.8
Cash And Money Market Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis	6.5	1.3
Available-for-sale securities, fair value	6.5	1.3
U.S. Equity Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis	8.0	5.4
Available-for-sale securities, fair value	11.1	7.4
International Equity Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis	4.2	3.4
Available-for-sale securities, fair value	4.9	3.8
Municipal Bond Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost basis	10.2	4.9
Available-for-sale securities, fair value	$ 10.2	$ 5.3