Fair Value Measurements - Schedule of Fair Values of Financial Liabilities (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Level 1 [Member]
Liabilities:
Long-term debt, including current portion	$ 0	$ 0
Preferred Stock	0	0
Total liabilities at fair value	0	0
Level 2 [Member]
Liabilities:
Long-term debt, including current portion	1,224.9	1,196.7
Preferred Stock	49.3	49.2
Total liabilities at fair value	1,274.2	1,245.9
Level 3 [Member]
Liabilities:
Long-term debt, including current portion	0	0
Preferred Stock	0	0
Total liabilities at fair value	0	0
Estimate of Fair Value, Fair Value Disclosure [Member]
Liabilities:
Long-term debt, including current portion	1,224.9	1,196.7
Preferred Stock	49.3	49.2
Total liabilities at fair value	1,274.2	1,245.9
Carrying Value [Member]
Liabilities:
Long-term debt, including current portion	1,227.9	1,167.3
Preferred Stock	48.5	48.4
Total liabilities at fair value	$ 1,276.4	$ 1,215.7