Other Comprehensive Income (Changes in Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Other Comprehensive Income [Abstract]
Unrealized gains (losses) arising during period , Pre-Tax	$ 124.1	$ (128.2)	$ 282.0	$ (73.5)
Amount of realized gains from sales and other, Pre-tax	(4.5)	(14.4)	(27.3)	(26.4)
Portion of other-than-temporary impairment losses recognized in earnings, Pre-tax	5.0	1.9	25.9	4.6
Net unrealized gains (losses), Pre-tax	124.6	(140.7)	280.6	(95.3)
Net actuarial losses and prior service cost arising in the period, Pre-tax		(4.2)		(1.2)
Amortization of net actuarial loss and prior service cost recognized as net periodic benefit cost, Pre-tax	2.5	4.7	5.0	7.3
Net pension and postretirement benefits, Pre-tax	2.5	0.5	5.0	6.1
Foreign currency translation recognized during the period, Pre-tax	(1.1)	11.9	(2.0)	(3.4)
Other comprehensive income (loss), Pre-tax	126.0	(128.3)	283.6	(92.6)
Unrealized gains (losses) arising during period , Tax Benefit (Expense)	(43.3)	44.8	(98.6)	25.7
Amount of realized gains from sales and other, Tax Benefit (Expense)	(2.5)	1.9	0.6	3.3
Portion of other-than-temporary impairment losses recognized in earnings, Tax Benefit (Expense)	(1.8)	(0.7)	(9.1)	(1.6)
Net unrealized gains (losses), Tax Benefit (Expense)	(47.6)	46.0	(107.1)	27.4
Net actuarial losses and prior service cost arising in the period, Tax Benefit (Expense)		0.9		(0.2)
Amortization of net actuarial loss and prior service cost recognized as net periodic benefit cost, Tax Benefit (Expense)	(0.8)	(1.3)	(1.7)	(2.2)
Net pension and postretirement benefits, Tax	(0.8)	(0.4)	(1.7)	(2.4)
Foreign currency translation recognized during the period, Tax Benefit (Expense)	0.4	(4.2)	0.7	1.2
Other comprehensive income (loss), Tax Benefit (Expense)	(48.0)	41.4	(108.1)	26.2
Unrealized gains (losses) arising during period , Net of Tax	80.8	(83.4)	183.4	(47.8)
Amount of realized gains from sales and other, Net of Tax	(7.0)	(12.5)	(26.7)	(23.1)
Portion of other-than-temporary impairment losses recognized in earnings, Net of Tax	3.2	1.2	16.8	3.0
Net unrealized gains (losses), Net of Tax	77.0	(94.7)	173.5	(67.9)
Net actuarial losses and prior service cost arising in the period, Net of Tax		(3.3)		(1.4)
Amortization of net actuarial loss and prior service cost recognized as net periodic benefit cost, Net of Tax	1.7	3.4	3.3	5.1
Net pension and postretirement benefits, Net of Tax	1.7	0.1	3.3	3.7
Foreign currency translation recognized during the period, Net of Tax	(0.7)	7.7	(1.3)	(2.2)
Other comprehensive income (loss), Net of Tax	$ 78.0	$ (86.9)	$ 175.5	$ (66.4)