CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement of Comprehensive Income [Abstract]
Net actuarial gain (loss) arising during period, tax	$ 20.3	$ (6.2)	$ (17.9)
Curtailment arising during period, tax	0	0	(0.2)
Settlement effects arising during period, tax	0	0	0.3
Less: amortization of actuarial loss, tax	3.6	2.8	2.2
Less: amortization of prior service credit, tax	(0.5)	(0.5)	(0.5)
Net gains on investment securities, tax	2.1	0.2	0.2
Net gains (losses) on derivatives, tax	$ 1.8	$ (2.1)	$ (1.1)