Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Loss) Reclassification Adjustments (Parantheticals) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Accumulated Other Comprehensive Income (Loss) Reclassification Adjustments (Parantheticals) [Abstract]
Net holding gain on investment securities arising during the period, tax expense (benefit)	$ 61.0	$ (207.8)	$ 128.5	$ (205.4)
Reclassification adjustment for net realized gain on investment securities, tax expense	19.2	14.5	30.0	17.1
Non-credit component of other than temporary impairments on investments, tax expense (benefit)	(0.3)	0	0	1.2
Cash flow hedges, holding gain, tax expense	0.4	0.4	0.8	0.8
Net change in unrecognized periodic benefit costs for defined benefit pension and postretirement benefit plans, tax expense	2.3	4.5	4.2	8.9
Foreign currency translation adjustment, tax expense (benefit)	(0.1)	0.3	(0.1)	(0.2)
Net gain recognized in other comprehensive income, tax expense	$ 82.5	$ (188.1)	$ 163.4	$ (177.6)