Employee and Agent Benefits - Weighted Average Assumptions (Details) - USD ($) $ in Millions	5 Months Ended	7 Months Ended	12 Months Ended
	May 31, 2019	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension benefits
Weighted-average assumptions used to determine benefit obligations as disclosed under the Obligations and Funded Status section
Discount rate: Benefit obligation (as a percent)		3.25%	3.25%	4.15%
Weighted-average assumptions used to determine net periodic benefit cost
Discount rate: Net periodic benefit cost (as a percent)	4.15%	3.70%	3.70%	3.60%	4.15%
Expected long-term return on plan assets: Net periodic benefit cost (as a percent)			5.95%	6.30%	6.70%
Pension benefits, Cash balance benefit
Weighted-average assumptions used to determine benefit obligations as disclosed under the Obligations and Funded Status section
Rate of compensation increase: Benefit obligation (as a percent)		4.95%	4.95%	4.94%
Weighted-average assumptions used to determine net periodic benefit cost
Rate of compensation increase: Net periodic benefit cost (as a percent)			4.94%	4.96%	5.02%
Pension benefits, Traditional benefit
Weighted-average assumptions used to determine benefit obligations as disclosed under the Obligations and Funded Status section
Rate of compensation increase: Benefit obligation (as a percent)		2.98%	2.98%	2.73%
Weighted-average assumptions used to determine net periodic benefit cost
Rate of compensation increase: Net periodic benefit cost (as a percent)			2.73%	2.77%	2.82%
Other postretirement benefits
Weighted-average assumptions used to determine benefit obligations as disclosed under the Obligations and Funded Status section
Discount rate: Benefit obligation (as a percent)		2.95%	2.95%	3.95%
Weighted-average assumptions used to determine net periodic benefit cost
Discount rate: Net periodic benefit cost (as a percent)			3.95%	3.35%	3.75%
Expected long-term return on plan assets: Net periodic benefit cost (as a percent)			5.19%	4.85%	4.40%
Rate of compensation increase: Net periodic benefit cost (as a percent)				2.39%	2.44%
Assumed Health Care Cost Trend Rates
Health care cost trend rate assumed for next year under age 65 (as a percent)		6.75%	6.75%	7.00%
Health care cost trend rate assumed for next year age 65 and over (as a percent)		6.00%	6.00%	6.00%
Rate to which the health care cost trend rate is assumed to decline (the ultimate trend rate) (as a percent)		4.50%	4.50%	4.50%
Year that the health care cost trend rate reaches the ultimate trend rate under age 65 (calendar year)			2029	2026
Year that the health care cost trend rate reaches the ultimate trend rate age 65 and over (calendar year)			2026	2025
Effect of one-percentage-point change in assumed health care cost trend rates
Effect on accumulated postretirement benefit obligation of a one-percentage-point increase in assumed health care cost trend rates			$ (1.2)
Effect on accumulated postretirement benefit obligation of a one-percentage-point decrease in assumed health care cost trend rates			$ 1.1
Home office medical and life plans
Weighted-average assumptions used to determine net periodic benefit cost
Expected long-term return on plan assets: Net periodic benefit cost (as a percent)			5.25%
Agent medical and life plans
Weighted-average assumptions used to determine net periodic benefit cost
Expected long-term return on plan assets: Net periodic benefit cost (as a percent)			4.95%
Long-term care plans
Weighted-average assumptions used to determine net periodic benefit cost
Expected long-term return on plan assets: Net periodic benefit cost (as a percent)			4.35%
Post-65 medical plans
Weighted-average assumptions used to determine net periodic benefit cost
Expected long-term return on plan assets: Net periodic benefit cost (as a percent)			5.00%