Employee and Agent Benefits - Pension Plan Changes and Plan Gains/Losses (Details) - Pension benefits $ in Millions	3 Months Ended
Mar. 31, 2020 USD ($)
Contributions
Contributions made by employer to fund qualified and nonqualified pension plans	$ 5.7
Maximum
Contributions
Amount of possible contributions to be made during the current fiscal year to the qualified and nonqualified pension plans combined	$ 35.0

Amount of contribution received by defined benefit plan from employer which increases plan assets.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
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Name:	us-gaap_DefinedBenefitPlanContributionsByEmployer
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration