Employee and Agent Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended			3 Months Ended	12 Months Ended							3 Months Ended	12 Months Ended			1 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2010 Pension benefits	Dec. 31, 2012 Pension benefits	Dec. 31, 2011 Pension benefits	Dec. 31, 2010 Pension benefits	Dec. 31, 2012 Qualified defined benefit pension plans	Dec. 31, 2011 Qualified defined benefit pension plans	Dec. 31, 2012 Nonqualified defined benefit pension plans	Dec. 31, 2011 Nonqualified defined benefit pension plans	Dec. 31, 2010 Other postretirement benefits	Dec. 31, 2012 Other postretirement benefits	Dec. 31, 2011 Other postretirement benefits	Dec. 31, 2010 Other postretirement benefits	Sep. 30, 2010 Retiree health benefits	Dec. 31, 2012 Retiree health benefits
Components of Net Periodic Benefit Cost (Income)
Service cost					$ 47.0	$ 44.0	$ 45.6	$ 42.3	$ 39.3	$ 4.7	$ 4.7		$ 1.3	$ 1.2	$ 8.8
Interest cost					109.1	108.5	105.7	92.8	91.7	16.3	16.8		8.2	8.9	18.1
Expected return on plan assets					(114.6)	(114.4)	(98.4)	(114.6)	(114.4)				(33.5)	(34.1)	(30.6)
Amortization of prior service (benefit) cost					(9.4)	(9.7)	(10.1)	(6.3)	(6.5)	(3.1)	(3.2)		(28.6)	(29.3)	(9.1)
Recognized net actuarial (gain) loss					90.9	65.8	67.6	84.8	61.2	6.1	4.6		0.9	0.4	4.1
Amount recognized due to special events					(0.7)	(1.4)	(0.9)	(0.4)	(0.9)	(0.3)	(0.5)		(3.5)	(5.1)	(2.6)
Net periodic benefit cost (income)					122.3	92.8	109.5	98.6	70.4	23.7	22.4		(55.2)	(58.0)	(11.3)
Eligibility age					21 years								57 years
Period of employment used to calculate average annual compensation for the final average pay benefit					5 years
Eligibility service period													10 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
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%
Change in benefit obligation
Benefit obligation at beginning of year					(2,158.4)	(1,933.8)							(165.1)	(162.6)
Service cost					(47.0)	(44.0)							(1.3)	(1.2)
Interest cost					(109.1)	(108.5)							(8.2)	(8.9)
Actuarial gain (loss)					(407.1)	(151.3)							21.2	2.6
Participant contributions													(6.6)	(6.4)
Benefits paid					76.4	73.6							13.0	13.9
Amount recognized due to special events												(0.2)		(0.4)
Plan amendment																153.6
Early retiree reinsurance program reimbursement														(1.2)
Other changes in benefit obligation					7.2	5.6							(0.8)	(0.9)
Benefit obligation at end of year				(1,933.8)	(2,638.0)	(2,158.4)	(1,933.8)					(162.6)	(147.8)	(165.1)	(162.6)
Change in plan assets
Fair value of plan assets at beginning of year					1,429.0	1,417.7		1,429.0					466.6	471.7
Actual return on plan assets					222.6	4.1							58.6	1.3
Employer contribution					106.9	80.8							0.9	1.1
Participant contributions													6.6	6.4
Benefits paid					(76.4)	(73.6)							(13.0)	(13.9)
Fair value of plan assets at end of year				1,417.7	1,682.1	1,429.0	1,417.7	1,682.1	1,429.0			471.7	519.7	466.6	471.7
Amount recognized in statement of financial position
Amount recognized in other assets													372.5	301.7
Amount recognized in other liabilities					(955.9)	(729.4)		(557.7)	(405.9)	(398.2)	(323.5)		(0.6)	(0.2)
Total assets (liabilities) recognized in statement of financial position					(955.9)	(729.4)		(557.7)	(405.9)	(398.2)	(323.5)		371.9	301.5
Amount recognized in accumulated other comprehensive (income) loss
Total net actuarial (gain) loss					861.2	660.0		725.0	586.3	136.2	73.7		(7.1)	40.1
Prior service (benefit) cost					(20.4)	(30.5)		(12.5)	(19.2)	(7.9)	(11.3)		(82.1)	(114.1)
Pre-tax accumulated other comprehensive (income) loss					840.8	629.5		712.5	567.1	128.3	62.4		(89.2)	(74.0)
Additional defined benefit plan disclosures
Accumulated benefit obligation					2,469.1	2,027.8
Market value of assets held in Rabbi trusts for benefit of nonqualified pension plan participants										300.8	281.2
Medicare subsidies received, accrued and included in service cost													0.8	0.9	0.8
Impact from Exit of Group Medical Insurance Business
Curtailment (gain) loss				(0.9)	(0.7)	(1.4)						(2.6)	(3.5)	(5.1)
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					2,638.0	2,158.4
Accumulated benefit obligation for defined benefit plans with an accumulated benefit obligation in excess of plan assets					2,469.1	2,027.8							1.7	1.5
Fair value of plan assets for defined benefit plans with an accumulated benefit obligation in excess of plan assets					1,682.1	1,429.0							1.1	1.3
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					292.1	256.0		223.5	243.3	68.6	12.7		(46.4)	30.6
Amortization of net gain (loss)					(90.9)	(65.8)		(84.8)	(61.2)	(6.1)	(4.6)		(0.9)	(0.7)
Amortization of prior service benefit (cost)					10.1	11.1		6.7	7.3	3.4	3.8		32.1	34.7
Total recognized in pre-tax accumulated other comprehensive (income) loss	196.1	266.0	(320.0)		211.3	201.3		145.4	189.4	65.9	11.9		(15.2)	64.6
Total recognized in net periodic benefit cost and pre-tax accumulated other comprehensive (income) loss					333.6	294.1		244.0	259.8	89.6	34.3		(70.4)	6.6
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					118.5								1.0
Estimated prior service cost (benefit) that will be amortized from accumulated other comprehensive income into net periodic benefit cost during the next fiscal year					$ (8.7)								$ (25.9)