Employee and Agent Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Contributions
Minimum annual contribution required in current fiscal year for qualified pension plan			$ 0
The low end of the range of possible contributions to be made during the current fiscal year to the qualified and nonqualified pension plans combined	69.0		69.0
The high end of the range of possible contributions to be made during the current fiscal year to the qualified and nonqualified pension plans combined	110.0		110.0
Contributions made by employer to fund qualified and nonqualified pension plans	23.0		69.0
Pension benefits
Components of Net Periodic Benefit Cost (Income)
Service cost	11.7	10.7	35.2	32.5
Interest cost	27.3	27.3	81.8	81.3
Expected return on plan assets	(28.6)	(29.7)	(85.9)	(87.2)
Amortization of prior service (benefit) cost	(2.4)	(2.4)	(7.0)	(7.4)
Recognized net actuarial (gain) loss	22.7	14.0	68.1	43.0
Amount recognized due to special events		(0.3)		(1.0)
Net periodic benefit cost (income)	30.7	19.6	92.2	61.2
Other postretirement benefits
Components of Net Periodic Benefit Cost (Income)
Service cost	0.3	0.3	1.0	0.9
Interest cost	2.0	2.3	6.1	6.7
Expected return on plan assets	(8.3)	(8.8)	(25.1)	(26.1)
Amortization of prior service (benefit) cost	(7.2)	(7.3)	(21.5)	(22.1)
Recognized net actuarial (gain) loss	0.3	0.1	0.7	0.3
Amount recognized due to special events		(1.1)		(4.0)
Net periodic benefit cost (income)	$ (12.9)	$ (14.5)	$ (38.8)	$ (44.3)