Employee and Agent Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended							3 Months Ended	12 Months Ended			1 Months Ended
	Dec. 31, 2010 Pension benefits	Dec. 31, 2011 Pension benefits Y	Dec. 31, 2010 Pension benefits	Dec. 31, 2009 Pension benefits	Dec. 31, 2011 Qualified defined benefit pension plans	Dec. 31, 2010 Qualified defined benefit pension plans	Dec. 31, 2011 Nonqualified defined benefit pension plans	Dec. 31, 2010 Nonqualified defined benefit pension plans	Dec. 31, 2010 Other postretirement benefits	Dec. 31, 2011 Other postretirement benefits Y	Dec. 31, 2010 Other postretirement benefits	Dec. 31, 2009 Other postretirement benefits	Sep. 30, 2010 Retiree health benefits	Dec. 31, 2011 Retiree health benefits
Components of Net Periodic Benefit Cost (Income)
Service cost		$ 44.0	$ 45.6	$ 51.4	$ 39.3	$ 39.3	$ 4.7	$ 6.3		$ 1.2	$ 8.8	$ 11.3
Interest cost		108.5	105.7	100.8	91.7	88.2	16.8	17.5		8.9	18.1	19.7
Expected return on plan assets		(114.4)	(98.4)	(79.5)	(114.4)	(98.4)				(34.1)	(30.6)	(25.9)
Amortization of prior service (benefit) cost		(9.7)	(10.1)	(7.7)	(6.5)	(6.6)	(3.2)	(3.5)		(29.3)	(9.1)	(2.1)
Recognized net actuarial (gain) loss		65.7	67.6	92.6	61.1	62.5	4.6	5.1		0.4	4.1	9.3
Amount recognized due to special events		(1.4)	(0.9)		(0.9)	(0.6)	(0.5)	(0.3)		(5.1)	(2.6)
Net periodic benefit cost (income)		92.7	109.5	157.6	70.3	84.4	22.4	25.1		(58.0)	(11.3)	12.3
Eligibility age (in years)		21								57
Period of employment used to calculate average annual compensation for the final average pay benefit (in years)		5
Eligibility service period (in years)										10
Maximum age used to calculate a partial benefit accrual of final average pay benefits (in years)		65
Minimum years of potential service used to calculate a partial benefit accrual of final average pay benefits (in years)		35
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		(1,933.8)	(1,797.4)							(162.6)	(360.1)
Service cost		(44.0)	(45.6)							(1.2)	(8.8)
Interest cost		(108.5)	(105.7)							(8.9)	(18.1)
Actuarial gain (loss)		(151.3)	(59.6)							2.6	62.5
Participant contributions										(6.4)	(6.0)
Benefits paid		73.6	70.2							13.9	15.3
Amount recognized due to special events										(0.4)	(0.2)
Plan amendment											153.6		153.6
Early retiree reinsurance program reimbursement										(1.2)
Other changes in benefit obligation		5.6	4.3							(0.9)	(0.8)
Benefit obligation at end of year	(1,933.8)	(2,158.4)	(1,933.8)	(1,797.4)					(162.6)	(165.1)	(162.6)	(360.1)
Change in plan assets
Fair value of plan assets at beginning of year		1,417.7	1,250.3		1,417.7					471.7	421.5
Actual return on plan assets		4.1	181.1							1.3	58.1
Employer contribution		80.8	56.5							1.1	1.4
Participant contributions										6.4	6.0
Benefits paid		(73.6)	(70.2)							(13.9)	(15.3)
Fair value of plan assets at end of year	1,417.7	1,429.0	1,417.7	1,250.3	1,429.0	1,417.7			471.7	466.6	471.7	421.5
Amount recognized in statement of financial position
Amount recognized in other assets									309.4	301.7	309.4
Amount recognized in other liabilities	(516.1)	(729.4)	(516.1)		(405.9)	(210.8)	(323.5)	(305.3)	(0.3)	(0.2)	(0.3)
Total assets (liabilities) recognized in statement of financial position	(516.1)	(729.4)	(516.1)		(405.9)	(210.8)	(323.5)	(305.3)	309.1	301.5	309.1
Amount recognized in accumulated other comprehensive (income) loss
Total net actuarial (gain) loss	469.7	660.0	469.7		586.3	404.1	73.7	65.6	10.2	40.1	10.2
Prior service (benefit) cost	(41.6)	(30.5)	(41.6)		(19.2)	(26.6)	(11.3)	(15.0)	(148.8)	(114.1)	(148.8)
Pre-tax accumulated other comprehensive (income) loss	428.1	629.5	428.1		567.1	377.5	62.4	50.6	(138.6)	(74.0)	(138.6)
Additional defined benefit plan disclosures
Accumulated benefit obligation	1,811.7	2,027.8	1,811.7
Market value of assets held in Rabbi trusts for benefit of nonqualified pension plan participants							281.2	265.3
Medicare subsidies received, accrued and included in service cost										0.9	0.8	0.8
Impact from Exit of Group Medical Insurance Business
Curtailment (gain) loss	(0.9)	(1.4)							(2.6)	(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	1,933.8	2,158.4	1,933.8
Accumulated benefit obligation for defined benefit plans with an accumulated benefit obligation in excess of plan assets	1,811.7	2,027.8	1,811.7						1.5	1.5	1.5
Fair value of plan assets for defined benefit plans with an accumulated benefit obligation in excess of plan assets	466.6	1,429.0	466.6						1.4	1.3	1.4
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		256.0	(27.5)		243.3	(28.4)	12.7	0.9		30.6	(89.8)
Prior service (benefit) cost											(153.7)
Amortization of net gain (loss)		(65.7)	(67.6)		(61.1)	(62.5)	(4.6)	(5.1)		(0.7)	(4.1)
Amortization of prior service benefit (cost)		11.1	11.0		7.3	7.3	3.8	3.7		34.7	11.7
Total recognized in pre-tax accumulated other comprehensive (income) loss		201.4	(84.1)		189.5	(83.6)	11.9	(0.5)		64.6	(235.9)
Total recognized in net periodic benefit cost and pre-tax accumulated other comprehensive (income) loss		294.1	25.4		259.8	0.8	34.3	24.6		6.6	(247.2)
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		90.8								0.9
Estimated prior service cost (benefit) that will be amortized from accumulated other comprehensive income into net periodic benefit cost during the next fiscal year		$ (9.4)								$ (28.6)