Fair Value Measurements Level 3 (Details) (Derivative Financial Instruments, Assets [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Derivative Financial Instruments, Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	$ 2.2	$ 4.9	$ 3.1	$ 3.7
Total realized/unrealized gains or (losses) included in non-operating income	3.7	4.0	4.8	11.1
Settlements	(3.5)	(4.4)	(5.5)	(10.3)
Balance at end of period	2.4	4.5	2.4	4.5
Total unrealized gains and (losses) included in non-operating income relating to assets and liabilities still on the consolidated balance sheet at period end	$ 0.3	$ (0.3)	$ (0.4)	$ 1.2