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, 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]	Accounting Standards Update 2016-13 [Member]
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 income	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 (loss)	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 income	(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 (loss)	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
Beginning balance at Dec. 31, 2020	5,954.8	2.9	0.6	1,956.8	3,548.7	709.8	(267.4)	3.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock plan issuances	11.8			11.8
Stock plan compensation expense	48.6			48.6
Common stock dividends	(118.5)				(118.5)
Acquisition of common stock	(581.6)			(127.2)	(454.4)
Net income	1,248.8				1,248.8
Preferred stock conversion		(2.9)	0.1	(141.8)			144.6
Preferred stock dividends	(4.7)				(4.7)
Change in equity of non-controlling interests	(4.0)				(0.6)			(3.4)
Acquisition of non-controlling interests	(16.9)			(16.9)
Other comprehensive income (loss)	(793.9)					(793.9)
Ending balance at Sep. 30, 2021	5,744.4	0.0	0.7	1,731.3	4,219.3	(84.1)	(122.8)	0.0
Beginning balance at Jun. 30, 2021	5,908.4	0.0	0.7	1,786.2	3,640.3	604.0	(122.8)	0.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock plan issuances	6.4			6.4
Stock plan compensation expense	18.2			18.2
Common stock dividends	(38.5)				(38.5)
Acquisition of common stock	(327.5)			(62.6)	(264.9)
Net income	882.4				882.4
Acquisition of non-controlling interests	(16.9)			(16.9)
Other comprehensive income (loss)	(688.1)					(688.1)
Ending balance at Sep. 30, 2021	$ 5,744.4	$ 0.0	$ 0.7	$ 1,731.3	$ 4,219.3	$ (84.1)	$ (122.8)	$ 0.0

[1] Amount relates to the adoption of the 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.