Employee and Agent Benefits (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Contributions
Minimum annual contribution required in current fiscal year for qualified pension plan			$ 0.0
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	$ 150.0		150.0
Contributions made by employer to fund qualified and nonqualified pension plans	25.2		67.8
Pension benefits
Components of Net Periodic Benefit Cost (Income)
Service cost	15.8	$ 13.5	47.4	$ 40.5
Interest cost	30.0	29.2	90.2	87.8
Expected return on plan assets	(40.2)	(33.0)	(120.5)	(99.0)
Amortization of prior service (benefit) cost	(0.5)	(1.0)	(1.4)	(3.4)
Recognized net actuarial (gain) loss	25.7	12.5	76.8	37.8
Net periodic benefit cost (income)	30.8	21.2	92.5	63.7
Other postretirement benefits
Components of Net Periodic Benefit Cost (Income)
Service cost	0.5	0.4	1.5	1.1
Interest cost	1.6	1.7	4.9	5.0
Expected return on plan assets	(8.5)	(8.2)	(25.5)	(24.5)
Amortization of prior service (benefit) cost	(4.6)	(5.0)	(13.8)	(15.2)
Recognized net actuarial (gain) loss	(0.3)	(1.0)	(0.7)	(2.7)
Net periodic benefit cost (income)	$ (11.3)	$ (12.1)	$ (33.6)	$ (36.3)