Credit Facility (Details)		3 Months Ended
		Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Line of Credit Facility [Line Items]
Amount outstanding at period end		$ 0	$ 30,000,000.0
Credit Facility
Line of Credit Facility [Line Items]
Debt Instrument, Term		1 year
Borrowing limit	[1]	$ 500,000,000
Amount outstanding at period end	[2]	$ 10,000,000
Number of extension you can request		2
Available		$ 490,000,000
Direct advances on the credit facility outstanding		0	0
Letter of Credit
Line of Credit Facility [Line Items]
Amount outstanding at period end		$ 10,000,000	$ 10,000,000

[1] This credit facility expires in June 2024.

[2] Includes outstanding commercial paper and letters of credit.