Employee and Agent Benefits (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
	May 31, 2019	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension benefits
Components of Net Periodic Benefit Cost (Income)
Service cost		$ 16.7	$ 18.2	$ 33.5	$ 36.5
Interest cost		32.1	29.9	64.9	59.8
Expected return on plan assets		(36.4)	(39.3)	(71.9)	(78.5)
Amortization of prior service (benefit) cost		(2.0)	(0.8)	(2.9)	(1.7)
Recognized net actuarial (gain) loss		17.2	16.9	34.1	33.8
Net periodic benefit cost (income)		27.6	24.9	57.7	49.9
Actuarial gain (loss)	$ (59.0)
Total plan amendment gain	122.4
Increase in benefit obligation	237.6
Asset gain on plan assets	$ 178.6
Contributions
Contributions made by employer to fund qualified and nonqualified pension plans		5.7		11.4
Pension benefits | Maximum
Contributions
Amount of possible contributions to be made during the current fiscal year to the qualified and nonqualified pension plans combined		25.0		25.0
Other postretirement benefits
Components of Net Periodic Benefit Cost (Income)
Interest cost		1.0	0.8	1.9	1.7
Expected return on plan assets		(8.3)	(8.4)	(16.6)	(16.8)
Amortization of prior service (benefit) cost		(0.3)	(3.4)	(0.6)	(6.9)
Recognized net actuarial (gain) loss			(0.4)		(0.7)
Net periodic benefit cost (income)		$ (7.6)	$ (11.4)	$ (15.3)	$ (22.7)