Note Payable (Narrative) (Details) $ in Millions		12 Months Ended
	Feb. 04, 2019 extension	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Debt Disclosure
Number of lines of credit		1	1
Aggregate borrowing capacity		$ 300	$ 225
Accordian feature available amount		$ 300	50
Line of credit facility, term		5 years
Note payable		$ 39	$ 32
Number of one year extensions | extension	2
Ratio of debt-to-total capital maximum		0.35
Minimum
Debt Disclosure
Line of credit, interest rate		2.59%	2.45%
Maximum
Debt Disclosure
Line of credit, interest rate		3.41%	4.75%