Consolidated Statements of Changes in Equity (unaudited) - USD ($) $ in Millions	Total	Preferred Stock	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Non-controlling Interests	Cumulative Effect, Period of Adoption, Adjustment	[1]	Cumulative Effect, Period of Adoption, Adjustment Retained Earnings	[1]
Beginning balance at Dec. 31, 2018	$ 5,133.9	$ 2.9	$ 1.6	$ 4,495.6	$ 5,759.7	$ (155.4)	$ (4,992.4)	$ 21.9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock plan issuances	7.1			7.1
Stock plan compensation expense	40.7			40.7
Common stock dividends	(113.0)				(113.0)
Acquisition of common stock	(185.0)			(18.9)			(166.1)
Net loss	258.0				255.0			3.0
Preferred stock dividends	(14.0)				(14.0)
Change in equity of non-controlling interests	2.1				(4.8)			6.9
Other comprehensive income	560.6					560.6
Ending balance at Sep. 30, 2019	5,690.4	2.9	1.6	4,524.5	5,882.9	405.2	(5,158.5)	31.8
Beginning balance at Jun. 30, 2019	5,760.3	2.9	1.6	4,509.2	5,980.9	328.7	(5,093.1)	30.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock plan issuances	3.6			3.6
Stock plan compensation expense	15.0			15.0
Common stock dividends	(37.3)				(37.3)
Acquisition of common stock	(68.7)			(3.3)			(65.4)
Net loss	(53.2)				(54.8)			1.6
Preferred stock dividends	(4.7)				(4.7)
Change in equity of non-controlling interests	(1.1)				(1.2)			0.1
Other comprehensive income	76.5					76.5
Ending balance at Sep. 30, 2019	5,690.4	2.9	1.6	4,524.5	5,882.9	405.2	(5,158.5)	31.8
Beginning balance at Dec. 31, 2019	$ 5,682.1	2.9	1.6	4,537.7	5,966.4	411.5	(5,267.3)	29.3	$ (20.4)		$ (20.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Stock plan issuances	$ 8.6			8.6
Stock plan compensation expense	41.9			41.9
Common stock dividends	(115.1)				(115.1)
Acquisition of common stock	(172.5)			(19.3)			(153.2)
Net loss	303.7				302.6			1.1
Preferred stock dividends	(14.0)				(14.0)
Change in equity of non-controlling interests	(18.7)				6.5			(25.2)
Acquisition of non-controlling interests	(2.3)			(0.7)				(1.6)
Other comprehensive income	246.7					246.7
Ending balance at Sep. 30, 2020	5,940.0	2.9	1.6	4,568.2	6,126.0	658.2	(5,420.5)	3.6
Beginning balance at Jun. 30, 2020	5,984.5	2.9	1.6	4,550.4	6,194.4	568.9	(5,350.4)	16.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock plan issuances	4.7			4.7
Stock plan compensation expense	15.5			15.5
Common stock dividends	(37.5)				(37.5)
Acquisition of common stock	(71.8)			(1.7)			(70.1)
Net loss	(30.5)				(30.2)			(0.3)
Preferred stock dividends	(4.7)				(4.7)
Change in equity of non-controlling interests	(7.2)				4.0			(11.2)
Acquisition of non-controlling interests	(2.3)			(0.7)				(1.6)
Other comprehensive income	89.3					89.3
Ending balance at Sep. 30, 2020	$ 5,940.0	$ 2.9	$ 1.6	$ 4,568.2	$ 6,126.0	$ 658.2	$ (5,420.5)	$ 3.6

[1] Amount relates to the adoption of a new accounting standard for accounting for expected credit losses for assets held at amortized cost, which established allowances for such expected credit losses as of January 1, 2020. Refer to Notes 3 and 7 for additional information.