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Equity (Schedule of Stock Offering Program) (Details) - USD ($)
$ / shares in Units, $ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
At The Market Stock Offering [Line Items]      
Stock Issued During Period, Shares, New Issues [1] 24,964,000    
Proceeds, net of fees (in millions) $ 848.2 $ 336.7 $ 23.1
At The Market Program      
At The Market Stock Offering [Line Items]      
Stock Issued During Period, Shares, New Issues 8,883,014 11,931,376 0
Common Stock Issued Average Price Per Share $ 26.85 $ 26.58 $ 0.00
Proceeds, net of fees (in millions) $ 232.5 $ 314.7 $ 0.0
[1] See Note 12, "Equity," for additional information.