Benefit Plans - Pension plan assets narrative (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension plans' assets
Expected weighted average long-term rate of return on primary employee plan assets for the next fiscal year	10 years
Expected weighted average long-term rate of return on employee-agent plan assets for the next fiscal year	5 years
Pension benefits
Pension plans' assets
Notional amount of derivatives, minimum percentage of plan assets	115.00%
Expected weighted average long-term rate of return on plan assets	7.34%	7.33%	7.32%
Expected weighted average long-term rate of return on plan assets for the next fiscal year	7.08%
Arithmetic average of the annual actual return on plan assets for the last 10 years	10.00%
Arithmetic average of the annual actual return on plan assets for the last 5 years	9.60%