Retirement Plans - Narrative (Details) - Nonqualified Plan - Pension Benefits - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Mar. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Pension plan contribution	$ 5
Defined benefit plan, expected contributions by employer remainder of year		$ 5

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

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Name:	us-gaap_DefinedBenefitPlanContributionsByEmployer
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration