Fair Value Measurements - Fair Value of Financial Assets and Financial Liabilities (Detail) (Fair Value, Measurements, Recurring [Member], USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Investments, Fair Value Disclosure	$ 83.5	$ 91.7
Derivative Liability	(45.1)	(165.9)
Fair Value, Inputs, Level 1 [Member]
Investments, Fair Value Disclosure	83.5	91.7
Derivative Liability	0	0
Fair Value, Inputs, Level 2 [Member]
Investments, Fair Value Disclosure	0	0
Derivative Liability	(45.1)	(165.9)
Fair Value, Inputs, Level 3 [Member]
Investments, Fair Value Disclosure	0	0
Derivative Liability	0	0
Equity Securities [Member]
Investments, Fair Value Disclosure	15.1	19.6
Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Investments, Fair Value Disclosure	15.1	19.6
Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Investments, Fair Value Disclosure	0	0
Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Investments, Fair Value Disclosure	0	0
US Treasury and Government [Member]
Investments, Fair Value Disclosure	68.4	72.1
US Treasury and Government [Member] | Fair Value, Inputs, Level 1 [Member]
Investments, Fair Value Disclosure	68.4	72.1
US Treasury and Government [Member] | Fair Value, Inputs, Level 2 [Member]
Investments, Fair Value Disclosure	0	0
US Treasury and Government [Member] | Fair Value, Inputs, Level 3 [Member]
Investments, Fair Value Disclosure	$ 0	$ 0