Stockholders' Equity (Narrative) (Details) - USD ($) shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 11, 2018
Stockholders' Equity Note [Abstract]
Dividends paid			$ 116,600,000	$ 120,200,000
Stock repurchase program, authorized amount					$ 300,000,000.0
Shares repurchased (in shares)			4.0
Shares repurchased, value	$ 40,000,000.0	$ 149,400,000	$ 90,100,000	$ 242,000,000.0