Investments In Unconsolidated Affiliates (Equity Method Investment Summarized Financial Information, Statement of Operations) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Operating revenue	$ 90.8	$ 55.2	$ 173.9	$ 158.7
Operating expenses	48.6	39.5	115.0	120.5
Net income	$ 42.2	$ 15.7	$ 58.4	$ 38.2