Earnings Per Share (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions			1 Months Ended			9 Months Ended		12 Months Ended
	Oct. 16, 2017	Sep. 15, 2017	Sep. 30, 2017	Jul. 31, 2016	Nov. 30, 2015	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Repayments of long-term debt						$ 1,139.0	$ 1,175.0
Debt instrument			$ 4,473.0			$ 4,473.0		$ 4,684.0
Common stock, date dividend declared						Sep. 15, 2017
Common stock, date dividend to be paid		Oct. 16, 2017				Oct. 16, 2017
Common Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Shares issued				98,900,000
Price per share				$ 13.00
Proceeds from issuance of shares				$ 1,247.0
Series B Preferred Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Trading day period						20 days
Long-term Debt [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Debt instrument			4,433.0			$ 4,433.0		4,643.0
Long-term Debt [Member] | 2015 Term Loan due December 2020 [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Repayments of long-term debt			$ 327.0	375.0		$ 327.0		423.0
Debt instrument					$ 750.0			$ 327.0
Debt instrument, term					3 years
Senior Notes [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Purchase of note principal				$ 700.0
Minimum [Member] | Depositary Shares [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Shares issued upon conversion			1.85014			1.85014
Minimum [Member] | Series B Preferred Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Shares issued upon conversion			37.0028			37.0028
Potential number of shares issued upon conversion						63,829,830
Maximum [Member] | Depositary Shares [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Shares issued upon conversion			2.17391			2.17391
Maximum [Member] | Series B Preferred Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Shares issued upon conversion			43.4782			43.4782
Potential number of shares issued upon conversion						74,999,895
Subsequent Event [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Common stock, shares issued as stock dividend	3,346,703
Common stock dividend, setteled in cash	$ 7.9