Stockholders' Equity (Details 2) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Other Comprehensive Income (Loss)
Other comprehensive income (loss), pre-tax	$ (227.5)	$ (262.3)	$ (724.8)	$ 373.4
Other comprehensive income (loss), tax	15.8	36.4	141.3	(183.3)
Other comprehensive income (loss)	(211.7)	(225.9)	(583.5)	190.1
Net unrealized gains (losses) on available-for-sale securities including NCI
Other Comprehensive Income (Loss)
Other comprehensive income (loss) before reclassifications, pre-tax	(191.9)	(301.8)	(999.0)	1,009.9
Adjustments for assumed changes in amortization patterns, pre-tax	35.7	28.2	118.1	(71.0)
Adjustments for assumed changes in policyholder liabilities, pre-tax	190.5	149.8	547.8	(434.7)
Other comprehensive income (loss), pre-tax	41.1	(119.5)	(334.8)	446.8
Other comprehensive income (loss) before reclassifications, tax	66.4	103.8	340.7	(340.7)
Reclassification from accumulated other comprehensive income, tax	(2.5)	(1.4)	0.5	18.8
Adjustments for assumed changes in amortization patterns, tax	(12.5)	(9.8)	(41.3)	24.9
Adjustments for assumed changes in policyholder liabilities, tax	(64.2)	(47.0)	(186.1)	146.8
Other comprehensive income (loss), tax	(12.8)	45.6	113.8	(150.2)
Other comprehensive income (loss) before reclassifications, after-tax	(125.5)	(198.0)	(658.3)	669.2
Reclassification from accumulated other comprehensive income, after-tax	4.3	2.9	(1.2)	(38.6)
Adjustments for assumed changes in amortization patterns, after-tax	23.2	18.4	76.8	(46.1)
Adjustments for assumed changes in policyholder liabilities, after-tax	126.3	102.8	361.7	(287.9)
Other comprehensive income (loss)	28.3	(73.9)	(221.0)	296.6
Net unrealized gains (losses) on available-for-sale securities including NCI | Net realized capital gains (losses)
Other Comprehensive Income (Loss)
Reclassification from accumulated other comprehensive income, pre-tax	6.8	4.3	(1.7)	(57.4)
Noncredit component of impairment losses on fixed maturities available-for-sale including NCI
Other Comprehensive Income (Loss)
Other comprehensive income (loss) before reclassifications, pre-tax	1.1	14.7	28.0	82.6
Adjustments for assumed changes in amortization patterns, pre-tax		3.1	(1.3)	(5.3)
Adjustments for assumed changes in policyholder liabilities, pre-tax	0.3	(0.9)	0.5	(1.5)
Other comprehensive income (loss), pre-tax	1.4	16.9	27.2	75.8
Other comprehensive income (loss) before reclassifications, tax	(0.3)	(5.0)	(9.7)	(29.3)
Adjustments for assumed changes in amortization patterns, tax		(1.2)	0.5	1.9
Adjustments for assumed changes in policyholder liabilities, tax	(0.1)	0.3	(0.1)	0.5
Other comprehensive income (loss), tax	(0.4)	(5.9)	(9.3)	(26.9)
Other comprehensive income (loss) before reclassifications, after-tax	0.8	9.7	18.3	53.3
Adjustments for assumed changes in amortization patterns, after-tax		1.9	(0.8)	(3.4)
Adjustments for assumed changes in policyholder liabilities, after-tax	0.2	(0.6)	0.4	(1.0)
Other comprehensive income (loss)	1.0	11.0	17.9	48.9
Net unrealized gains (losses) on derivative instruments including NCI
Other Comprehensive Income (Loss)
Other comprehensive income (loss) before reclassifications, pre-tax	21.7	48.4	50.1	67.7
Reclassification from accumulated other comprehensive income, pre-tax	(4.3)	(1.8)	(22.1)	6.3
Adjustments for assumed changes in amortization patterns, pre-tax	6.0	(8.4)	18.5	(8.9)
Adjustments for assumed changes in policyholder liabilities, pre-tax	(7.2)	6.9	(12.0)	0.4
Other comprehensive income (loss), pre-tax	16.2	45.1	34.5	65.5
Other comprehensive income (loss) before reclassifications, tax	(7.6)	(17.0)	(17.5)	(23.8)
Reclassification from accumulated other comprehensive income, tax	1.3	0.6	7.3	(2.4)
Adjustments for assumed changes in amortization patterns, tax	(2.1)	2.9	(6.5)	3.1
Adjustments for assumed changes in policyholder liabilities, tax	2.5	(2.4)	4.2	(0.1)
Other comprehensive income (loss), tax	(5.9)	(15.9)	(12.5)	(23.2)
Other comprehensive income (loss) before reclassifications, after-tax	14.1	31.4	32.6	43.9
Reclassification from accumulated other comprehensive income, after-tax	(3.0)	(1.2)	(14.8)	3.9
Adjustments for assumed changes in amortization patterns, after-tax	3.9	(5.5)	12.0	(5.8)
Adjustments for assumed changes in policyholder liabilities, after-tax	(4.7)	4.5	(7.8)	0.3
Other comprehensive income (loss)	10.3	29.2	22.0	42.3
Foreign currency translation adjustment including NCI
Other Comprehensive Income (Loss)
Other comprehensive income (loss), pre-tax	(306.5)	(210.3)	(512.6)	(231.2)
Other comprehensive income (loss), tax	43.3	14.5	74.3	22.8
Other comprehensive income (loss)	(263.2)	(195.8)	(438.3)	(208.4)
Unrecognized postretirement benefit obligation including NCI
Other Comprehensive Income (Loss)
Other comprehensive income (loss), pre-tax	20.3	5.5	60.9	16.5
Other comprehensive income (loss) before reclassifications, tax	(8.4)	(1.9)	(25.0)	(5.8)
Other comprehensive income (loss), tax	(8.4)	(1.9)	(25.0)	(5.8)
Other comprehensive income (loss) before reclassifications, after-tax	11.9	3.6	35.9	10.7
Other comprehensive income (loss)	11.9	3.6	35.9	10.7
Unrecognized postretirement benefit obligation including NCI | Operating expense
Other Comprehensive Income (Loss)
Other comprehensive income (loss) before reclassifications, pre-tax	$ 20.3	$ 5.5	$ 60.9	$ 16.5