Accumulated Other Comprehensive Income (Loss) (Other Comprehensive Income (Loss) Reclassification Adjustments) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net holding loss on investment securities arising during the period, net of tax benefit of $223.6, $5.4 and $38.2, respectively	$ (407.2)	$ (3.2)	$ (71.6)
Reclassification adjustment for net realized gain on investment securities, net of tax expense of ($60.6), ($104.0) and ($49.6), respectively	112.5	193.1	92.2
Total reclassification adjustment on investments	(294.7)	189.9	20.6
Non-credit component of OTTI on investments, net of tax (expense) benefit of ($0.9), ($2.4) and $0.5, respectively	1.7	4.5	(0.7)
Holding gain (loss), net of tax (expense) benefit of ($1.6), ($0.1) and $5.3, respectively	3.0	0.1	(10.0)
Net change in unrecognized periodic benefit costs for defined benefit pension and postretirement benefit plans, net of tax (expense) benefit of ($106.8), ($7.1) and $81.7, respectively	172.7	(10.9)	(119.8)
Foreign currency translation adjustment, net of tax expense of ($0.6), ($0.3) and ($0.2), respectively	1.4	0.6	0.2
Net (loss) gain recognized in other comprehensive income, net of tax benefit (expense) of $53.1, ($108.5) and $75.9, respectively	$ (115.9)	$ 184.2	$ (109.7)