Other Equity Matters (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended				6 Months Ended
	Jan. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Apr. 21, 2020
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount								$ 200.0
Preferred Stock, Redemption Price Per Share		$ 25.00				$ 25.00
Dividends		$ 35.8	$ 37.1	$ 38.6	$ 40.4
Cash dividends paid per share		$ 0.52	$ 0.52	$ 0.52	$ 0.52	1.04	$ 1.04
Common Stock [Member]
Class of Stock [Line Items]
Treasury Stock Acquired, Average Cost Per Share						$ 28.19
Treasury Stock, Carrying Basis		$ 96.3				$ 96.3
Stock Repurchase Program, Remaining Authorized Repurchase Amount		164.0				164.0
Preferred Stock [Member]
Class of Stock [Line Items]
Cumulative unpaid preferred dividends		1.8				$ 1.8
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Dividends		$ 1.8	$ 1.8	$ 1.8
Preferred Stock, Dividends, Per Share, Cash Paid		$ 0.53125	$ 0.53125	$ 0.53125
Series B Preferred Stock [Member]
Class of Stock [Line Items]
Dividends		$ 2.9	$ 2.9
Preferred Stock, Dividends, Per Share, Cash Paid		$ 0.50	$ 0.50
Series C Preferred Stock [Member]
Class of Stock [Line Items]
Dividends		$ 3.2	$ 3.2
Preferred Stock, Dividends, Per Share, Cash Paid		$ 0.46094	$ 0.46094
Series D Preferred Stock [Member]
Class of Stock [Line Items]
Proceeds from Issuance of Preferred Stock, Preference Stock, and Warrants	$ 145.3
Preferred Units, Offering Costs	$ 4.7
Dividends		$ 2.6	$ 1.5
Preferred Stock, Dividends, Per Share, Cash Paid		$ 0.42969	$ 0.24349
Treasury Stock [Member]
Class of Stock [Line Items]
Treasury shares acquired, shares		2,050,924	1,365,620	2,347,826	2,636,534	3,416,544