Employee and Agent Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Components of Net Periodic Benefit Cost (Income)
Participant contributions as a percent of expected cost of coverage for employees hired prior to January 1, 2002, who retired on or after January 1, 2011 (as a percent)	60.00%
Other changes recognized in accumulated other comprehensive (income) loss
Total recognized in pre-tax accumulated other comprehensive (income) loss	$ 423.4	$ (511.6)	$ 196.1
Pension benefits
Components of Net Periodic Benefit Cost (Income)
Service cost	54.0	57.1	47.0
Interest cost	117.1	103.8	109.1
Expected return on plan assets	(131.9)	(127.4)	(114.6)
Amortization of prior service (benefit) cost	(4.7)	(8.7)	(9.4)
Recognized net actuarial (gain) loss	50.5	118.5	90.9
Amount recognized due to special events			(0.7)
Net periodic benefit cost (income)	85.0	143.3	122.3
Eligibility age	21 years
Period of employment used to calculate average annual compensation for the final average pay benefit	5 years
Maximum age used to calculate a partial benefit accrual of final average pay benefits	65 years
Minimum years of potential service used to calculate a partial benefit accrual of final average pay benefits	35 years
Change in benefit obligation
Benefit obligation at beginning of year	(2,440.2)	(2,638.0)
Service cost	(54.0)	(57.1)
Interest cost	(117.1)	(103.8)
Actuarial gain (loss)	(532.9)	279.2
Benefits paid	84.2	79.5
Benefit obligation at end of year	(3,060.0)	(2,440.2)	(2,638.0)
Change in plan assets
Fair value of plan assets at beginning of year	1,925.6	1,682.1
Actual return on plan assets	246.0	199.8
Employer contribution	130.9	123.2
Benefits paid	(84.2)	(79.5)
Fair value of plan assets at end of year	2,218.3	1,925.6	1,682.1
Amount recognized in statement of financial position
Amount recognized in other liabilities	(841.7)	(514.6)
Total assets (liabilities) recognized in statement of financial position	(841.7)	(514.6)
Amount recognized in accumulated other comprehensive (income) loss
Total net actuarial (gain) loss	759.2	391.1
Prior service (benefit) cost	(6.9)	(11.8)
Pre-tax accumulated other comprehensive (income) loss	752.3	379.3
Additional defined benefit plan disclosures
Accumulated benefit obligation	2,854.0	2,287.4
Impact from Exit of Group Medical Insurance Business
Curtailment (gain) loss			(0.7)
Information for Defined Benefit Plans With an Accumulated Benefit Obligation in Excess of Plan Assets
Projected benefit obligation for defined benefit plans with an accumulated benefit obligation in excess of plan assets	3,060.0	2,440.2
Accumulated benefit obligation for defined benefit plans with an accumulated benefit obligation in excess of plan assets	2,854.0	2,287.4
Fair value of plan assets for defined benefit plans with an accumulated benefit obligation in excess of plan assets	2,218.3	1,925.6
Plan actuarial gain and loss amortization disclosures
Allowable corridor not used for amortization of actuarial gains and losses of qualified pension plan (as a percent)	10.00%
Other changes recognized in accumulated other comprehensive (income) loss
Net actuarial (gain) loss	418.8	(351.7)
Amortization of net gain (loss)	(50.5)	(118.5)
Amortization of prior service benefit (cost)	4.7	8.7
Total recognized in pre-tax accumulated other comprehensive (income) loss	373.0	(461.5)
Total recognized in net periodic benefit cost and pre-tax accumulated other comprehensive (income) loss	458.0	(318.2)
Estimated amounts that will be amortized from accumulated other comprehensive income into net periodic benefit cost during the next fiscal year
Estimated net actuarial (gain) loss that will be amortized from accumulated other comprehensive income into net periodic benefit cost during the next fiscal year	102.3
Estimated prior service cost (benefit) that will be amortized from accumulated other comprehensive income into net periodic benefit cost during the next fiscal year	(1.9)
Qualified defined benefit pension plans
Components of Net Periodic Benefit Cost (Income)
Service cost	46.8	50.4
Interest cost	99.1	88.2
Expected return on plan assets	(131.9)	(127.4)
Amortization of prior service (benefit) cost	(3.1)	(6.1)
Recognized net actuarial (gain) loss	42.9	104.4
Net periodic benefit cost (income)	53.8	109.5
Change in plan assets
Fair value of plan assets at beginning of year	1,925.6
Fair value of plan assets at end of year	2,218.3	1,925.6
Amount recognized in statement of financial position
Amount recognized in other liabilities	(385.3)	(138.6)
Total assets (liabilities) recognized in statement of financial position	(385.3)	(138.6)
Amount recognized in accumulated other comprehensive (income) loss
Total net actuarial (gain) loss	603.1	298.3
Prior service (benefit) cost	(3.4)	(6.5)
Pre-tax accumulated other comprehensive (income) loss	599.7	291.8
Other changes recognized in accumulated other comprehensive (income) loss
Net actuarial (gain) loss	347.8	(322.4)
Amortization of net gain (loss)	(42.9)	(104.4)
Amortization of prior service benefit (cost)	3.1	6.1
Total recognized in pre-tax accumulated other comprehensive (income) loss	308.0	(420.7)
Total recognized in net periodic benefit cost and pre-tax accumulated other comprehensive (income) loss	361.8	(311.2)
Nonqualified defined benefit pension plans
Components of Net Periodic Benefit Cost (Income)
Service cost	7.2	6.7
Interest cost	18.0	15.6
Amortization of prior service (benefit) cost	(1.6)	(2.6)
Recognized net actuarial (gain) loss	7.6	14.1
Net periodic benefit cost (income)	31.2	33.8
Amount recognized in statement of financial position
Amount recognized in other liabilities	(456.4)	(376.0)
Total assets (liabilities) recognized in statement of financial position	(456.4)	(376.0)
Amount recognized in accumulated other comprehensive (income) loss
Total net actuarial (gain) loss	156.1	92.8
Prior service (benefit) cost	(3.5)	(5.3)
Pre-tax accumulated other comprehensive (income) loss	152.6	87.5
Additional defined benefit plan disclosures
Market value of assets held in Rabbi trusts for benefit of nonqualified pension plan participants	329.6	304.3
Other changes recognized in accumulated other comprehensive (income) loss
Net actuarial (gain) loss	71.0	(29.3)
Amortization of net gain (loss)	(7.6)	(14.1)
Amortization of prior service benefit (cost)	1.6	2.6
Total recognized in pre-tax accumulated other comprehensive (income) loss	65.0	(40.8)
Total recognized in net periodic benefit cost and pre-tax accumulated other comprehensive (income) loss	96.2	(7.0)
Other postretirement benefits
Components of Net Periodic Benefit Cost (Income)
Service cost	1.4	1.0	1.3
Interest cost	6.6	5.7	8.2
Expected return on plan assets	(32.6)	(28.8)	(33.5)
Amortization of prior service (benefit) cost	(20.3)	(25.9)	(28.6)
Recognized net actuarial (gain) loss	(3.4)	1.0	0.9
Amount recognized due to special events			(3.5)
Net periodic benefit cost (income)	(48.3)	(47.0)	(55.2)
Eligibility age	57 years
Eligibility service period	10 years
Change in benefit obligation
Benefit obligation at beginning of year	(140.6)	(147.8)
Service cost	(1.4)	(1.0)
Interest cost	(6.6)	(5.7)
Actuarial gain (loss)	(26.0)	7.9
Participant contributions	(6.6)	(6.8)
Benefits paid	12.2	13.6
Other changes in benefit obligation	(0.7)	(0.8)
Benefit obligation at end of year	(169.7)	(140.6)	(147.8)
Change in plan assets
Fair value of plan assets at beginning of year	613.0	519.7
Actual return on plan assets	31.9	95.9
Employer contribution	0.4	4.2
Participant contributions	6.6	6.8
Benefits paid	(12.2)	(13.6)
Fair value of plan assets at end of year	639.7	613.0	519.7
Amount recognized in statement of financial position
Amount recognized in other assets	470.7	473.0
Amount recognized in other liabilities	(0.7)	(0.6)
Total assets (liabilities) recognized in statement of financial position	470.0	472.4
Amount recognized in accumulated other comprehensive (income) loss
Total net actuarial (gain) loss	(53.0)	(83.1)
Prior service (benefit) cost	(35.9)	(56.2)
Pre-tax accumulated other comprehensive (income) loss	(88.9)	(139.3)
Additional defined benefit plan disclosures
Medicare subsidies received, accrued and included in service cost	0.7	0.8	0.8
Impact from Exit of Group Medical Insurance Business
Curtailment (gain) loss			(3.5)
Information for Defined Benefit Plans With an Accumulated Benefit Obligation in Excess of Plan Assets
Accumulated benefit obligation for defined benefit plans with an accumulated benefit obligation in excess of plan assets	1.5	1.5
Fair value of plan assets for defined benefit plans with an accumulated benefit obligation in excess of plan assets	0.8	0.9
Other changes recognized in accumulated other comprehensive (income) loss
Net actuarial (gain) loss	26.7	(75.0)
Amortization of net gain (loss)	3.4	(1.0)
Amortization of prior service benefit (cost)	20.3	25.9
Total recognized in pre-tax accumulated other comprehensive (income) loss	50.4	(50.1)
Total recognized in net periodic benefit cost and pre-tax accumulated other comprehensive (income) loss	2.1	(97.1)
Estimated amounts that will be amortized from accumulated other comprehensive income into net periodic benefit cost during the next fiscal year
Estimated net actuarial (gain) loss that will be amortized from accumulated other comprehensive income into net periodic benefit cost during the next fiscal year	(0.8)
Estimated prior service cost (benefit) that will be amortized from accumulated other comprehensive income into net periodic benefit cost during the next fiscal year	$ (18.4)