Other Assets - Restricted Investments (Details) - Restricted - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Investments
Expense for fair value of assets, less expenses, allocated to participants			$ 1.2	$ 1.1
Maximum
Investments
Gain (loss) on assets	$ 0.1	$ (0.1)	$ 0.1	$ (0.1)

Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), investment in debt security measured at amortized cost (held-to-maturity) and investment in debt security measured at fair value with change in fair value recognized in net income (trading).

No definition available.

Name:	us-gaap_DebtSecuritiesRealizedGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration