Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Employee benefit plans, tax effect:
Prior service credit and net losses arising during the period, tax effect	$ 0	$ 0	$ 0.2	$ 0.8
Reclassification adjustment for amortization to net periodic pension cost, tax effect	0.9	0.5	2.6	1.3
Other comprehensive income, tax effect:
Tax effect on unrealized capital gains (losses) on securities-available-for-sale	19.5	40.1	40.6	53.2
Reclassification adjustment for net capital gains included in net income, tax effect	$ (1.0)	$ (0.1)	$ (1.8)	$ (2.6)