Common Stockholders' Equity (Schedule of Changes in Shares of Common Stock Outstanding) (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Common Stock Shares Outstanding [Roll Forward]
Balance, beginning of year	182,993,640	182,272,278	181,790,399
Shares issued	687,339	1,257,762	1,578,384
Shares repurchased	(269,072)	(536,400)	(1,096,505)
Balance, end of year	183,411,907	182,993,640	182,272,278