Note Payable (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Debt Disclosure
Number of lines of credit	1
Aggregate borrowing capacity	$ 300
Accordian feature available amount	300
Note payable	$ 54	$ 39
Ratio of debt-to-total capital maximum	0.35
Minimum
Debt Disclosure
Line of credit, interest rate	1.03%	2.59%
Maximum
Debt Disclosure
Line of credit, interest rate	4.25%	3.41%