Investments Allowance for Credit Losses - Aging of Past-Due Receivables (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Financing Receivable, Recorded Investment, Past Due [Line Items]
Recorded investment in impaired notes receivable, past due	$ 0.0
Minimum [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Period Required For Considering Financing Receivable As Non Accrual Status	60 days
Period for placing financing receivables on non-accrual status	89 days
Maximum [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Period Required For Considering Financing Receivable As Non Accrual Status	89 day