Employee and Agent Benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
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	81.0		81.0
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	27.0		81.0
Pension benefits
Components of Net Periodic Benefit Cost (Income)
Service cost	14.3	11.7	42.9	35.2
Interest cost	25.9	27.3	77.7	81.8
Expected return on plan assets	(31.8)	(28.6)	(95.6)	(85.9)
Amortization of prior service (benefit) cost	(2.1)	(2.4)	(6.3)	(7.0)
Recognized net actuarial (gain) loss	29.5	22.7	88.6	68.1
Net periodic benefit cost (income)	35.8	30.7	107.3	92.2
Other postretirement benefits
Components of Net Periodic Benefit Cost (Income)
Service cost	0.3	0.3	0.9	1.0
Interest cost	1.4	2.0	4.2	6.1
Expected return on plan assets	(7.2)	(8.3)	(21.6)	(25.1)
Amortization of prior service (benefit) cost	(6.5)	(7.2)	(19.5)	(21.5)
Recognized net actuarial (gain) loss	0.3	0.3	0.9	0.7
Net periodic benefit cost (income)	$ (11.7)	$ (12.9)	$ (35.1)	$ (38.8)