Permanent and Temporary Equity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Aug. 01, 2018
Equity [Abstract]
Equity offering program, authorized offering amount				$ 1,000.0
Stock issued during period, shares, new issues, equity offering program	0	1,100,000	18,900,000
Equity offering program, remaining authorized offering amount	$ 1,000.0
Stock issued during period, value, new issues, equity offering program		$ 73.9	$ 1,300.0
Common stock outstanding percentage of beneficial ownership acquired threshold for excess shares	9.00%
Preferred stock outstanding percentage of beneficial ownership acquired threshold for excess shares	9.90%
Maximum deferral payment period of purchase price for excess shares	5 years
Number of excess shares held by trustee	0