Noncontrolling Interests Change in Ownership Interest Table (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Issuance 1 [Member]	Oct. 02, 2012 Issuance 1 [Member]
Noncontrolling Interest Owner [Line Items]
Limited Liability Corp Units Issued													5,294,118
Net income attributable to parent	$ 38.5	$ 185.5	$ 93.9	$ 37.1	$ 36.4	$ 178.7	$ 103.0	$ 24.8	$ 355.0	$ 342.9	$ 295.3
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Changes, Net									5.1			5.1
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Change Due to Net Income Attributable to Parent and Effects of Changes, Net									360.1
Consolidation Less Than Wholly Owned Subsidiary Parent Ownership Interest Changes Issuance of Equity By Subsidiary To Noncontrolling Interest Tax Effect													$ 3.2