Accumulated Other Comprehensive Income (Loss) (Reconciliation Of The Components Of Accumulated Other Comprehensive Income) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
investments, gross unrealized gains	$ 1,156.5	$ 1,324.3	$ 1,054.2
Investments, gross unrealized losses	(161.8)	(53.1)
Investments, net pretax unrealized gains	994.7	1,271.2
Deferred tax liability	(345.4)	(433.2)
Net unrealized gains on investments	649.3	838.0
Cash flow hedges, gross unrealized losses	(48.6)	(53.0)
Cash flow hedges, deferred tax asset	17.0	18.6
Net unrealized losses on cash flow hedges	(31.6)	(34.4)
Defined benefit pension plans, deferred net actuarial loss	(426.4)	(674.8)
Defined benefit pension plans, deferred prior service credits	8.4	3.7
Defined benefit pension plans, deferred tax asset	167.5	264.4
Net unrecognized periodic benefit costs for defined benefit pension plans	(250.5)	(406.7)
Postretirement benefit plans, deferred net actuarial loss	(154.7)	(188.3)
Postretirement benefit plans, deferred prior service credits	86.2	99.8
Defined benefit pension plans, deferred tax asset	27.4	34.8
Net unrecognized periodic benefit costs for postretirement benefit plans	(41.1)	(53.7)
Foreign currency translation adjustments, gross unrealized gains (losses)	2.0	(1.1)
Foreign currency translation adjustments, deferred tax (liability) asset	(0.7)	0.4
Net unrealized gains (losses) on foreign currency translation adjustments	1.3	(0.7)
Accumulated other comprehensive income	$ 327.4	$ 342.5	$ 183.2