Equity (Details) - USD ($) $ / shares in Units, shares in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2017	Sep. 30, 2016
Dividends Payable [Line Items]
Preferred Stock, Dividends, Per Share, Cash Paid		$ 18.1424
Common Stock, Dividends, Per Share, Cash Paid	[1]	$ 0.950	$ 0.950	$ 0.950
Dividends, Common Stock, Cash	[1]	$ 389,600,000	$ 350,300,000	$ 343,300,000
Dividends, Preferred Stock, Cash		$ 29,900,000.0
Common stock repurchased during period, shares					0.3
Purchases of capital stock					$ 23,037,000	$ 24,759,000
Common Stock [Member]
Dividends Payable [Line Items]
Dividends Payable, Date Declared	[1]	Aug. 03, 2017	May 18, 2017	Feb. 17, 2017
Dividends Payable, Date to be Paid	[1]	Sep. 29, 2017	Jun. 30, 2017	Mar. 31, 2017
Dividends Payable, Date of Record	[1]	Sep. 15, 2017	Jun. 16, 2017	Mar. 17, 2017
Preferred Stock [Member]
Dividends Payable [Line Items]
Dividends Payable, Date Declared		Sep. 21, 2017
Dividends Payable, Date to be Paid		Nov. 01, 2017
Dividends Payable, Date of Record		Oct. 15, 2017
At the Market Program [Member]
Dividends Payable [Line Items]
Payments of Stock Issuance Costs					$ 200,000

[1] Inclusive of dividends accrued for holders of unvested restricted stock units, which will be paid when and if the restricted stock units vest.