Equity (Share Activity) (Narrative) (Details) - USD ($) shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2018
Equity, Treasury Stock [Line Items]
Treasury stock acquired, value	$ 29,900,000		$ 128,300,000
2016 Share Repurchase Program [Member]
Equity, Treasury Stock [Line Items]
Treasury stock acquired, value		$ 98,400,000
2018 Share Repurchase Program [Member]
Equity, Treasury Stock [Line Items]
Share repurchase program, amount authorized, value		$ 100,000,000
Share repurchase program, amount available for future share repurchases, value	$ 70,000,000		$ 70,000,000
Treasury Stock, Common [Member]
Equity, Treasury Stock [Line Items]
Treasury stock acquired (in shares)	0.7		2.7
Treasury Stock, Common [Member] | 2016 Share Repurchase Program [Member]
Equity, Treasury Stock [Line Items]
Treasury stock acquired (in shares)		2.0
Treasury Stock, Common [Member] | 2018 Share Repurchase Program [Member]
Equity, Treasury Stock [Line Items]
Treasury stock acquired (in shares)	0.7