Accumulated Other Comprehensive Income (Reconciliation Of The Components Of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Available-for-sale Debt Securities, Accumulated Gross Unrealized Gain, before Tax	$ 815.0	$ 1,154.9
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(447.5)	(196.8)
Investments, Net pretax unrealized gains	367.5	958.1
Investments, Deferred tax liability	(124.2)	(330.5)
Net unrealized gains on investments	243.3	627.6
Non-credit components of OTTI on investments, Gross unrealized losses	(15.4)	(6.8)
Non-credit components of OTTI on investments, Deferred tax asset	5.4	2.4
Net unrealized non-credit component of OTTI on investments	(10.0)	(4.4)
Cash flow hedges, Gross unrealized losses	(124.8)	(55.2)
Cash flow hedges, Deferred tax asset	43.7	19.3
Net unrealized losses on cash flow hedges	(81.1)	(35.9)
Defined benefit pension plans, Deferred net actuarial loss	(635.0)	(563.7)
Defined benefit pension plans, Deferred prior service credits	0.1	2.2
Defined benefit pension plans, Deferred tax asset	250.4	223.2
Net unrecognized periodic benefit costs for defined benefit pension plans	(384.5)	(338.3)
Deferred Net Actuarial Loss Postretirement Benefit Plans	(162.7)	(211.2)
Deferred Prior Service Credit Postretirement Benefit Plans	73.5	88.0
Postretirement benefit plans, Deferred tax asset	35.1	48.9
Net unrecognized periodic benefit costs for postretirement benefit plans	(54.1)	(74.3)
Foreign currency translation adjustments, Gross unrealized losses	(9.5)	(4.3)
Foreign currency translation adjustments, Deferred tax asset	3.3	1.5
Net unrealized losses on foreign currency translation adjustment	(6.2)	(2.8)
Accumulated other comprehensive (loss) income	$ (292.6)	$ 171.9