Consolidated Statement of Stockholders' Equity (unaudited) - 6 months ended Jun. 30, 2018 - USD ($) $ in Millions		Total	Common Stock	Preferred Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income	Treasury Stock	Non-controlling Interest	Preferred Stock	Preferred Stock Preferred Stock	Preferred Stock Additional Paid-in Capital
Beginning balance at Dec. 31, 2017		$ 4,281.5	$ 1.5	$ 0.0	$ 3,197.9	$ 5,697.3	$ 234.0	$ (4,860.1)	$ 10.9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock plan exercises		(8.8)			(8.8)
Stock plan compensation		21.7		0.0	21.7
Common stock dividends		(60.6)				(60.6)
Net income		173.0				173.0
Issuance of preferred stock		975.5	0.1		975.4					$ 276.4	$ 2.9	$ 273.5
Issuance of common stock		975.5	0.1		975.4					$ 276.4	$ 2.9	$ 273.5
Preferred stock dividends		(4.8)				(4.8)
Change in equity of non-controlling interest		9.5							9.5
Other comprehensive income		(338.0)					(338.0)
Ending balance at Jun. 30, 2018		5,332.9	$ 1.6	$ 2.9	$ 4,459.7	5,846.3	(137.9)	$ (4,860.1)	$ 20.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of change in accounting principles, net of taxes | Accounting Standards Update 2016-01 and 2014-09	[1]	$ 7.5				$ 41.4	$ (33.9)

[1] Amounts relate to 1) the requirement to recognize the fair value changes of equity securities directly within income (resulting in a reclassification of unrealized gains as of December 31, 2017 between accumulated other comprehensive income ("AOCI") and retained earnings) and 2) the impact of adoption of the new revenue recognition standard for revenues from service contracts and sales of products. See Note 3 for additional information.