Accumulated Other Comprehensive Income (Loss) (Reconciliation Of The Components Of Accumulated Other Comprehensive Income) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Gross unrealized gains, available-for-sale investments	$ 1,003.0	$ 1,373.9	$ 1,282.1
Gross unrealized losses, available-for-sale investments	(276.7)	(46.7)
Net pre-tax unrealized gains, available-for-sale investments	726.3	1,327.2
Deferred tax liability	(249.7)	(465.0)
Net unrealized gains on investments	476.6	862.2
Unrealized losses non-credit component of OTTI on investments	(0.9)	(3.4)
Deferred tax asset, non-credit component of OTTI on investments	0.3	1.2
Net unrealized non-credit component of OTTI on investments	(0.6)	(2.2)
Gross unrealized losses, cash flow hedges	(50.8)	(55.4)
Deferred tax asset, cash flow hedges	17.8	19.4
Net unrealized losses on cash flow hedges	(33.0)	(36.0)
Deferred net actuarial loss, defined benefit pension plans	(654.0)	(620.3)
Deferred prior service credits, defined benefit pension plans	3.3	4.1
Deferred tax asset, defined benefit pension plans	256.4	249.6
Net unrecognized periodic benefit costs for defined benefit pension plans	(394.3)	(366.6)
Deferred net actuarial loss, postretirement benefit plans	(182.7)	(224.0)
Deferred prior service credits, postretirement benefit plans	93.2	106.5
Deferred tax asset, postretirement benefit plans	35.2	47.6
Net unrecognized periodic benefit costs for postretirement benefit Plans	(54.3)	(69.9)
Gross unrealized gains (losses), foreign currency translation adjustments	1.3	(0.9)
Deferred tax (liability) asset, foreign currency translation adjustments	(0.5)	0.3
Net unrealized gains (losses) on foreign currency translation adjustments	0.8	(0.6)
Accumulated other comprehensive (loss) income	$ (4.8)	$ 386.9	$ 299.1