Stockholders' Equity (DRSPP) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended		172 Months Ended
	Dec. 31, 2020	Sep. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2017	Aug. 08, 2013
Class of Stock [Line Items]
Common stock, shares authorized (in shares)	874,300,000		874,300,000	886,950,000
Issuance of stock, net of expenses (in shares)	12,300,000
DRSPP
Class of Stock [Line Items]
Common stock, shares authorized (in shares)						9,000,000.0
Shares of common stock authorized and available for issuance (in shares)	8,700,000		8,700,000
Issuance of stock, net of expenses (in shares)		379,903	235,635	322,888	34,614,403
Value of shares issued net of expenses		$ 2.8	$ 1.0	$ 2.4	$ 287.6