CONSOLIDATED STATEMENTS OF CHANGES IN OWNERS' EQUITY AND SERIES A PREFERRED STOCK (Unaudited) - USD ($) shares in Thousands, $ in Millions	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings (Accumulated Deficit) [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Shares [Member]	Noncontrolling Interests [Member]	Series A Preferred Stock [Member]
Balance at Dec. 31, 2016	$ 5,724.4	$ 0.2	$ 5,506.2	$ (187.3)	$ (38.3)	$ (32.2)	$ 475.8
Balance (in shares) at Dec. 31, 2016		184,721				514
Series A Preferred Stock at Dec. 31, 2016								$ 190.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Impact of accounting standard adoption (see Note 3)	56.1			56.1
Compensation on equity grants	10.8		10.8
Distribution equivalent rights	(2.2)		(2.2)
Shares issued under compensation program (in shares)		42
Shares and units tendered for tax withholding obligations	(0.5)					$ (0.5)
Shares and units tendered for tax withholding obligations (in shares)		(9)				9
Issuance of common stock	676.8		676.8
Issuance of common stock (in shares)		11,886
Receivables from common stock offerings	(19.6)		(19.6)
Series A Preferred Stock dividends
Dividends	(22.9)			(22.9)
Dividends in excess of retained earnings			(22.9)	22.9
Deemed dividends - accretion of beneficial conversion feature	(6.1)		(6.1)					6.1
Common stock dividends
Dividends	(176.6)			(176.6)
Dividends in excess of retained earnings			(176.6)	176.6
Distributions to noncontrolling interests	(12.5)						(12.5)
Contributions from noncontrolling interests	8.9						8.9
Other comprehensive income (loss)	44.8				44.8
Net income (loss)	(110.5)			(119.3)			8.8
Balance at Mar. 31, 2017	6,170.9	$ 0.2	5,966.4	(250.5)	6.5	$ (32.7)	481.0
Balance (in shares) at Mar. 31, 2017		196,640				523
Series A Preferred Stock at Mar. 31, 2017								196.9
Balance at Dec. 31, 2017	6,756.0	$ 0.2	6,302.8	(77.2)	(29.9)	$ (35.6)	595.7
Balance (in shares) at Dec. 31, 2017		217,567				586
Series A Preferred Stock at Dec. 31, 2017								216.5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Impact of accounting standard adoption (see Note 3)	5.2			5.2	(5.2)
Compensation on equity grants	13.2		13.2
Distribution equivalent rights	(3.3)		(3.3)
Shares issued under compensation program (in shares)		51
Shares and units tendered for tax withholding obligations	(0.4)					$ (0.4)
Shares and units tendered for tax withholding obligations (in shares)		(8)				8
Issuance of common stock	57.7		57.7
Issuance of common stock (in shares)		1,163
Exercise of warrants - share settled		59
Series A Preferred Stock dividends
Dividends	(22.9)			(22.9)
Dividends in excess of retained earnings			(22.9)	22.9
Deemed dividends - accretion of beneficial conversion feature	(7.0)		(7.0)					7.0
Common stock dividends
Dividends	(199.3)			(199.3)
Dividends in excess of retained earnings			(199.3)	199.3
Distributions to noncontrolling interests	(19.3)						(19.3)
Contributions from noncontrolling interests	280.1						280.1
Acquisition of related party (see Note 17)	1.2						1.2
Other comprehensive income (loss)	69.5				69.5
Net income (loss)	38.9			22.9			16.0
Balance at Mar. 31, 2018	$ 6,964.4	$ 0.2	$ 6,141.2	$ (49.1)	$ 34.4	$ (36.0)	$ 873.7
Balance (in shares) at Mar. 31, 2018		218,832				594
Series A Preferred Stock at Mar. 31, 2018								$ 223.5