CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Statement of Other Comprehensive Income [Abstract]
Prior service credit arising during period, tax	$ 0	$ 0	$ 2.0
Net actuarial loss arising during period, tax	(6.2)	(17.9)	(2.6)
Curtailment arising during period, tax	0	(0.2)	0
Settlement effects arising during period, tax	0	0.3	0
Less: amortization of actuarial loss, tax	2.8	2.2	2.1
Less: amortization of prior service credit, tax	(0.5)	(0.5)	(0.4)
Net gains on investment securities, tax	0.2	0.2	0.4
Net losses on derivatives, tax	$ (2.1)	$ (1.1)	$ (0.2)