CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Settlements tax	$ (37.3)	$ (62.2)	$ (87.3)	$ (202.6)
Ineffectiveness tax	0.6	0.2	0.9	(0.8)
Change in fair value of derivative instruments tax	5.0	(22.1)	19.7	62.7
Amortization of prior service cost included in net periodic pension cost tax	$ 0.2	$ 0.2	$ 0.5	$ 0.5